Non-aqueous secondary battery and its control methods

ABSTRACT

The invention provides a non-aqueous secondary battery having positive and negative electrodes and non-aqueous electrolyte containing lithium salt which has an energy capacity of 30 Wh or more, a volume energy density of 180 Wh/l or higher, which battery has a flat shape and is superior in heat radiation characteristic, used safely and particularly preferably used for a energy storage system. The invention also provides a control method of the secondary battery.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.09/700,988, filed Feb. 5, 2001, which is the U.S. National Phase under35 U.S.C. §371 of International Application PCT/JP99/02658, filed May20, 1999, which claims priority to Japanese Patent Application No.2002-26012, filed Feb. 1, 2002, which claims priority to Japanese PatentApplication No. 10-138347 filed May 20, 1998, No. 10-165373 filed Jun.12, 1998, No. 10-369928 filed Dec. 25, 1998, No. 10-369936 filed Dec.25, 1998, No. 10-369969 filed Dec. 25, 1998, No. 10-369986 filed Dec.25, 1998, No. 10-373667 filed Dec. 28, 1998, and No. 11-65072 filed Mar.11, 1999, the disclosure of which is herein incorporated by reference ittheir entirety. The International Application was not published underPCT Article 21(2) in English.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a non-aqueous secondary battery and itscontrol method, particularly to a non-aqueous secondary batterypreferably used for a energy storage system and its control method.

2. Description of the Prior Art

A household distributed power-storage system for storing nighttime powerand photovoltaic power and a energy storage system for an electricvehicle have been recently noticed from the viewpoints of effective useof energy for resource saving and global atmospheric problems. Forexample, Japanese Unexamined Patent Publication No. 6-86463 discloses atotal system constituted by combining a power supply from a powerstation, gas co-generation system, a fuel cell, and a storage battery asa system capable of supplying energy to energy consumers under anoptimum condition. A secondary battery used for the above energy storagesystem must be a large scale battery having a large capacity unlike asmall secondary battery for a portable devise having an energy capacityof 10 Wh or smaller. Therefore, the above energy storage system isnormally used as a battery system constituted by stacking a plurality ofsecondary batteries in series and having a voltage of 50 to 400 V and inmost cases, the system uses a lead-acid battery.

In the field of a small secondary battery for a portable devise, anickel-hydrogen battery and a lithium secondary battery are developed asnew batteries in order to correspond to the needs for a small size and alarge capacity and therefore, a battery having a volume energy densityof 180 Wh/l or more is marketed. Particularly, because a lithium ionbattery has a possibility of a volume energy density exceeding 350 Wh/land is superior to a lithium secondary battery using metal lithium as anegative electrode in reliabilities such as safety and cyclecharacteristic, the market of the battery has been remarkably expanded.

Therefore, also in the field of a large scale battery for a energystorage system, development is energetically progressed by LithiumBattery Energy Storage Technology Research Association (LIBES) or thelike by targeting a lithium ion battery as a prospective product of ahigh energy density battery.

The energy capacity of the large lithium ion battery approximatelyranges between 100 Wh and 400 Wh and the volume energy density of thebattery ranges between 200 and 300 Wh/l, which reaches the level of asmall secondary battery for a portable devise. Typical shapes of thebattery include a cylindrical shape having a diameter of 50 to 70 mm anda length of 250 to 450 mm and a prismatic shape such as an angular boxshape or a boxed shape with rounded edges having a thickness of 35 to 50mm.

Moreover, as a thin lithium secondary battery, the following aredisclosed: a film battery using a film obtained by laminating a metaland a plastic for a thin case and having a thickness of 1 mm or less(Japanese Unexamined Patent Publication Nos. 1993-159757 and 1995-57788)and a small prismatic battery having a thickness of 2 to 15 mm (JapaneseUnexamined Patent Publication Nos. 1996-195204, 1996-138727, and1997-213286). Purposes of these lithium secondary batteries correspondto decrease of a portable devise in size and thickness. For example, athin battery which has a thickness of several millimeters and an area ofapprox. JIS size A4 and which can be stored on the bottom of a portablepersonal computer is also disclosed (Japanese Unexamined PatentPublication No. 1993-283105). However, the thin battery has an energycapacity of 10 Wh or smaller that is too small as a secondary batteryfor a energy storage system.

Japanese Unexamined Patent Publication Nos. 1982-208079 and 1988-24555propose the use of graphite as a negative-electrode material for alithium secondary battery which is superior in flexibility and on whichmossy lithium is not deposited even in the case of repetition of acharge-discharge cycle. Because graphite has a special layer structureand a property of forming an inter-calation compound, it is practicallyused as an electrode material for a secondary battery using theproperty. Moreover, various types of carbon having a low crystallinitysuch as carbon having a disordered layer obtained by thermallydecomposing hydrocarbon in a gaseous phase and a selective orientationproperty are disclosed in Japanese Unexamined Patent Publication No.1988-24555 as materials in each of which an electrolyte is not easilydecomposed.

These negative-electrode materials have advantages and disadvantages.When using carbon having a high crystallinity such as graphite as anegative-electrode material, it is theoretically known that a change ofpotentials due to discharge of lithium ions is decreased and a capacityto be used for a battery increases. However, when the crystallinity ofthe carbon is increased, the charging rate is lowered probably due todecomposition of an electrolyte, and the carbon is broken due toexpansion/contraction of the plane interval of crystal caused byrepetition of charge and discharge.

Moreover, when using carbon having a low crystallinity as anegative-electrode material, a change of potentials due to discharge oflithium ions increases and thereby, a capacity usable for a batterydecreases, and thus, it is difficult to manufacture a battery having alarge capacity.

Japanese Unexamined Patent Publication No. 1992-368778 shows that it ispossible to prevent carbon from being broken by forming a doublestructure in which a carbon particle having a high crystallinity iscovered with carbon having a low crystallinity. When using carbonprepared by the above method as an active material, it is theoreticallypossible to obtain an electrode superior in potential smoothness andhaving a large capacity by preventing decomposition of an electrolyte.When attempting formation of a practical electrode by using thedouble-structure active-material particles, an electrode having athickness of 50 to 500 μm for a cylindrical battery by applying anactive material onto copper foil. However, the capacity per electrodevolume was not increased because the electrode density was not easilyraised. More specifically, it is difficult to raise the electrodedensity. If setting the electrode density to 1.20 g/cm³ or more throughpressure compression, a high volume capacity of 400 mAh/cm³ or more ofthe negative electrode cannot be resultantly obtained because thedouble-structure active material particles are broken.

In the case of a large lithium secondary battery (energy capacity of 30Wh or larger) for an energy storage system, a high energy density can beobtained. However, because the design of the battery is generallysimilar to the small battery for a portable devise, a cylindrical orprismatic battery is constituted which has a diameter or a thicknessthree times larger than those of a small battery for a portable devise.In this case, heat is easily stored in the battery due to Joule heatcaused by the internal resistance of the battery in charging ordischarging or internal heat of the battery due to change of the entropyof the active material due to insertion or detachment of lithium ions.Therefore, the difference between the temperature of the inner portionof the battery and the temperature nearby the surface of the batteryincreases and thereby, internal resistances differ. As a result, chargecapacity or voltage is easily fluctuated. Moreover, because two or morebatteries of this type are connected to make a battery module in use,capability of heat storage differs depending on a battery position inthe assembled system and fluctuation of heat storage between batteriesoccurs, and it is difficult to accurately control the whole of thebattery module. Furthermore, because heat radiation is likely to beinsufficient under high-rate charge/discharge, the battery temperaturerises and thereby the battery is brought under an undesirable state.Therefore, a problem is left in the viewpoint of deterioration ofservice life due to decomposition of an electrolyte, and lack ofreliability, particularly safety, because of the possibility of thermalrunaway of a battery.

To solve the above problem, in the case of a energy storage system foran electric vehicle, the following methods are disclosed: air coolingusing a cooling fan, a cooling method using a Peltier element (JapaneseUnexamined Patent Publication No. 1996-148189) and a method for packinga latent-heat storing material into a battery (Japanese UnexaminedPatent Publication No. 1997-219213). However, these methods use externalcooling and therefore do not provide essential solution to the problems.

Moreover, to obtain a high-capacity battery, it is desirable to set autilization factor of graphite-based particles used for a negativeelectrode to a value as high as possible. However, when improving theutilization factor, electrodeposition of lithium metal on a negativeelectrode increases and heat produced due to a reaction of anelectrolyte at approximately 150 degree in Celsius increases.Particularly, in the case of a large scale battery, a negative electrodehaving a higher capacity is requested in order to improve the energydensity and safety of the battery.

Furthermore, a separator having a thickness of 0.02 to 0.05 mm referredto as a micro-porous film made of polypropylene or polyethylene used fora commercially available lithium-ion secondary battery is a typicalseparator for the above lithium battery and it is locally attempted touse non-woven fabric of the above material for a separator.

In the case of a flat battery, the front and back surface areas of thebattery increase as the thickness of the battery decreases, and holdingforce to be incurred on the surfaces of the electrodes in the batterydecreases. Particularly, in the case of a large lithium secondarybattery (energy capacity of 30 Wh or larger) used for a energy storagesystem, the above phenomenon is remarcable. For example, in the case ofa 100 Wh-class lithium ion battery having a thickness of 6 mm, the frontand back surface areas of the battery reach a very large value of 600cm² (either side).

Therefore, when using the above separator for a flat battery having asmall holding force for pressing the surface of the electrodes, aproblem is left that cyclic deterioration is accelerated due to therepetition of charge and discharge.

Moreover, as internal structure of a general battery, positive andnegative electrodes and a separator for separating the electrodes fromeach other are layered. In the case of a lithium ion battery, a positiveelectrode made of metal oxide such as LiCoO₂, a negative electrode madeof carbon, such as graphite, which can be doped and undoped withlithium, and a separator referred to as micro-porous film made ofpolypropylene, polyethylene or the like and having a thickness of 0.02to 0.05 mm are different from each other in dimension. For example, inthe case of positive and negative electrodes, the negative electrode isdesigned so that it is slightly larger than the positive electrode toprevent electrodeposition of lithium metal on the negative electrode andto prevent fluctuation of the products even if faced positive andnegative electrodes are slightly shifted from each other when a batteryis assembled. Moreover, the separator is designed so that it is largerthan the positive and negative electrodes in order to prevent a shortcircuit.

In the case of a cylindrical battery, positioning of the positive andnegative electrodes and separators different from each other in size canbe easily contrived in the operation of a winder. However, when stackingelectrodes in a prismatic or box-shaped battery, the positioning isdifficult. Therefore, in such cases, layered electrodes are made bypressing electrodes wound into an ellipse configuration, or by layeringelectrodes after inserting them into a baggy separator. However, astacking method having a high packing efficiency of layers is desired.

Particularly, in the case of a flat battery, when using the method ofpressing wound electrodes, a short circuit occurs due to separation ofan electrode active-material layer from a current collector at anelectrode portion having a intensively pressed curvature. When using abaggy separator, sufficient pressure cannot be obtained because of alarge electrode area. Therefore, a gap is easily formed between aseparator and an electrode layer due to creases or the like of theseparator, and the internal resistance of the battery easily increases.Moreover, the binding margin of the separator increases in size and thepacking efficiency of the electrodes decreases, influencing the capacitydesign of the battery. In view of the above-described points, a stackingmethod realizing a high packing efficiency of electrodes is not foundwhich is suitable for a large scale battery or a flat large scalebattery, simplifies positioning of layers, and hardly causes a shortcircuit.

To control a secondary battery for a energy storage system, in the caseof an aqueous secondary battery such as a lead-acid battery ornickel-cadmium battery or the like, a plurality of single cells areconnected in series to constitute a module and a plurality of modulesare connected in series to constitute an assembly of batteries, in manycases. In these cases, charge and discharge operations are generallycontrolled per modules. By measuring voltage, temperature, current, andresistance of a module, the charge and discharge states and thedeterioration level of a battery are determined, and charge anddischarge are controlled in accordance with the determined results, inmany cases.

In the case of a lithium ion battery, even a commercially availablesmall secondary battery is generally controlled on cell by cell basis ina serial module (a module formed by serial connection of two cells ormore). This is because a lithium ion battery has a large weak point inovercharge and overdischarge. For example, the safety of a cell becomeunsecured only by an overcharge state of several tens of mV, andovercharge or overdischarge fatally deteriorates a cycle life.

As described in Japanese Unexamined Patent Publication Nos. 1996-182212and 1997-28042, a lithium ion battery for a energy storage system isalso controlled on cell by cell basis. The single-cell control is themost advanced art among the battery control methods currently disclosedand is partly introduced into aqueous batteries for an energy storagesystem.

In the case of a large secondary battery (energy capacity of 30 Wh orlarger) for a energy storage system, the capacity, volume, and electrodearea for each single cell are ten times or more as large as those of asmall battery for a portable devise and the fluctuation of operationalcharacteristics in a single cell, which is not a large problem for asmall secondary battery, reaches a level which cannot be ignored.Particularly, in the case of a large lithium secondary battery, thefluctuation of operational characteristics in a single cell is large andgreatly influences the safety and reliability similarly to thefluctuation of operational characteristics between single cells of asmall lithium ion battery.

Specifically, there are many fluctuations to be considered in a singlecell such as electrode deterioration, contact pressure applied to anelectrode, and current intensity in a current collector in the singlecell. In the case of the above cylindrical and prismatic batteries(batteries having thickness and diameter three times or more as large asthose of small battery for a portable devise), heat is easily stored inthe batteries because of Joule heat due to the internal resistance ofthe batteries during charge or discharge, or because of internallyproduced heat of the batteries due to entropy change of active materialscaused by insertion and detachment of lithium ion. Therefore, thedifference between the temperature inner portion of the battery and thetemperature nearby the surface of the battery is large, and thus theinternal resistance showing temperature dependency differs, and thecharge capacity and voltage are likely to fluctuate in a single cell.

However, because the large lithium secondary battery art of this type isgenerally similar to a small lithium ion secondary battery, attempts onbattery design and charge and discharge control considering thefluctuation in a single cell are not made yet. Such attempts are notapplied to aqueous secondary batteries such as a lead-acid battery,nickel-cadmium secondary battery, nickel-hydrogen secondary battery,which are generally controlled per module.

SUMMARY OF THE INVENTION

It is a main object of the present invention to provide a non-aqueoussecondary battery having a large capacity of 30 Wh or larger and avolume energy density of 180 Wh/l or higher and superior in radiationcharacteristic and safety.

It is another object of the present invention to provide a flatnon-aqueous secondary battery which can maintain the superiorcharacteristics during cyclic operation.

It is still another object of the present invention to provide a flatnon-aqueous secondary battery which facilitates the stacked structureand prevents the formation of a short circuit when the battery isassembled.

It is still another object of the present invention to provide asecondary battery for a energy storage system superior in reliabilitysuch as safety and cyclic durability, and a method for controlling thesame.

Other features of the present invention will become more apparent fromthe following description.

To achieve the above objects, the present invention provides a flatnon-aqueous secondary battery comprising positive and negativeelectrodes and a non-aqueous electrolyte containing lithium salt andhaving an energy capacity of 30 Wh or larger and a volume energy densityof 180 Wh/l or higher. It is preferable that this secondary battery isflat and has a thickness of less than 12 mm.

In the present invention, positive- and negative-electrode activematerials are not limited. However, it is preferable to apply A-, B-,and C-type negative electrodes having the following structures.Particularly, when using manganese oxide compound such as lithiummanganese oxide or the like as a positive-electrode active material, theabove negative electrodes have a high effect as described below.

(A-Type Negative Electrode)

Negative electrode formed by using graphite having an average particlediameter of 1 to 50 μm as active-material particles, a resin as abinder, and a metal as a current collector and having a porosity of 20to 3.5%, an electrode density of 1.40 to 1.70 g/cm³, and an capacity ofelectrode of 400 mAh/cm³ or higher.

(B-Type Negative Electrode)

Negative electrode comprising as active material double-structuregraphite particles formed with graphite-based particles and amorphouscarbon layers covering the surface of the graphite-based particles, thegraphite-based particles having (d002) spacing of (002) planes of notmore than 0.34 nm as measured by X-ray wide-angle diffraction method,the amorphous carbon layers having (d002) spacing of (002) planes of0.34 nm or larger.

(C-Type Negative Electrode)

Negative electrode comprising as active material a carbon materialmanufactured by mixing at least one of artificial graphite and naturalgraphite with a carbon material having volatile components on thesurface and/or in the inside and heat treatment of the mixture.

In the present invention, when a secondary battery is provided with aseparator, it is preferable to use A- or B-type separator or a separatorcapable of positioning an electrode unit having the following structurerespectively.

(A-Type Separator)

A separator in which when a pressure of 2.5 kg/cm² is applied to thedirection of thickness of the separator, the thickness A of theseparator is not less than 0.02 mm and not more than 0.15 mm and theporosity of the separator is 40% or higher, and when the absolute valueof a change rate of the thickness (mm) of the separator relative to thepressure (kg/cm²) applied to the direction of thickness of the separatoris defined as B (mm/(kg/cm²)), the pressure F which renders B/A=1 is notless than 0.05 kg/cm² and not

more than 1 kg/cm².

(B-Type Separator)

A separator having a first separator and a second separator differentfrom the first separator, wherein when a pressure of 2.5 kg/cm² isapplied to the direction of thickness of the separator, the thickness Aof the first separator is not less than 0.02 mm and not more than 0.15mm and the porosity of the first separator is 40% or higher, and whenthe absolute value of a change rate of the thickness (mm) of the firstseparator relative to the pressure (kg/cm²) applied to the direction ofthickness of the first separator is defined as B (mm/(kg/cm²)), thepressure F which renders B/A=1 is not less than 0.05 kg/cm² and not morethan 1 kg/cm², and the second separator is a micro-porous film having athickness of 0.05 mm or less, a pore diameter of 5 mm or less, and aporosity of 25% or more.

(Separator Capable of Positioning Electrode Unit)

A separator bonded with a positive and/or negative electrode.

The above objects of the present invention are also achieved by asecondary-battery operation control method comprising the steps ofmeasuring operational parameters of at different portions of the batteryand controlling operations of the battery based on the results of themeasurement.

Furthermore, the above objects of the present invention are achieved bya secondary battery for a energy storage system, comprising positive andnegative terminals for charge and discharge provided on the battery caseand operation-parameter measuring electrodes extending from differentportions of the battery to the outside of the battery case formeasurement of the operation parameters in the battery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top view and a side view of a non-aqueous secondarybattery of an embodiment of the present invention, which is used for aenergy storage system;

FIG. 2 shows a side view of stacked electrodes to be stored in thebattery shown in FIG. 1;

FIG. 3 illustrates a manufacturing method of a conventional smallprismatic battery;

FIG. 4 illustrates a method for manufacturing the bottom case shown inFIG. 1;

FIG. 5 illustrates another method for manufacturing a battery case of anon-aqueous secondary battery of the present invention;

FIG. 6 shows an electrode used in an embodiment of a non-aqueoussecondary battery of the present invention;

FIG. 7 is a graph showing results of measurement of the thickness of anA-type separator while applying a pressure in the thickness direction ofthe separator;

FIG. 8 shows a side view and a perspective view of a B-type separator;

FIG. 9 shows a side view and a perspective view of another B-typeseparator;

FIG. 10 shows a side view of stacked electrodes including a C-typeseparator;

FIG. 11 shows side views of electrode units including a C-typeseparator;

FIG. 12 is illustrations for explaining an electrode unit including aC-type separator;

FIG. 13 is a perspective view of a secondary battery to be applied to acontrol method of the present invention;

FIG. 14 is a block diagram of a control system of the secondary batteryshown in FIG. 13;

FIG. 15 shows a front view (a) and a top view (b) of an electrode of thesecondary battery shown in FIG. 13;

FIG. 16 shows a front view (a) and a top view (b) of a secondary batterystoring electrodes shown in FIG. 15;

FIG. 17 is an enlarged front view of an stacked electrodes in thesecondary battery shown in FIG. 16;

FIG. 18 shows a front view (a) and a top view (b) of another electrodefor the secondary batteries shown above;

FIG. 19 is an enlarged front view of stacked electrodes using theelectrode shown in FIG. 18; and

FIG. 20 is a top view of a secondary battery storing electrodes shown inFIG. 18.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A non-aqueous secondary battery of an embodiment of the presentinvention is described below by referring to the accompanying drawings.FIG. 1 shows a top view and a side view of a flat rectangular(notebook-type) non-aqueous secondary battery for a energy storagesystem, and FIG. 2 is a side view of stacked electrodes to be stored inthe battery shown in FIG. 1.

As shown in FIGS. 1 and 2, the non-aqueous secondary battery of thisembodiment is provided with a battery case (battery vessel) comprising aupper case 1 and a bottom case 2 and an electrode-stacked bodycomprising a plurality of positive electrodes 101 a and negativeelectrodes 101 b and 101 c and a separator 104 stored in the batterycase. In the case of the flat non-aqueous secondary battery of thisembodiment, the positive electrode 101 a and the negative electrode 101b (or the negative electrode 101 c formed at the both sides of thestacked body), for example, are alternately arranged and stacked withthe separator 104 positioned therebetween as shown in FIG. 2. However,the present invention is not limited to the above arrangement. It ispossible to change the number of layers correspondingly to a requiredcapacity etc.

The positive-electrode current collector of each positive electrode 101a is electrically connected to a positive-electrode tab 3 via apositive-electrode tab 103 a and similarly, negative-electrode currentcollectors of the each negative electrodes 101 b and 101 c areelectrically connected to a negative-electrode tab 4 via anegative-electrode tab 103 b. The positive-electrode tab 3 andnegative-electrode tab 4 are mounted on the battery case, that is, theupper case 1 while insulated therefrom . The entire circumferences ofthe upper case 1 and the bottom case 2 are welded at the point A shownby the enlarged view in FIG. 1. The upper case 1 is provided with asafety vent 5 for releasing the internal pressure in the battery whenthe pressure rises. The non-aqueous secondary battery shown in FIGS. 1and 2 has, for example, a length of 300 mm, a width of 210 mm, and athickness of 6 mm. A lithium secondary battery using LiMn₂O₄ for thepositive electrode 101 a and graphite described below for the negativeelectrodes 101 b and 101 c has, for example, an energy capacity of 80 to100 Wh and it can be used for a energy storage system.

The non-aqueous secondary battery constituted as described above can beused for a household energy storage system (for nighttime power storage,co-generation, photovoltaic power generation, or the like) and a energystorage system of an electric vehicle or the like and have a largecapacity and a high energy density. In this case, the energy capacity ispreferably kept at 30 Wh or larger, more preferably kept at 50 Wh orlarger, and the energy density is preferably kept at 180 Wh/l or higher,or more preferably kept at 200 Wh/l or higher. When the battery has anenergy capacity of smaller than 30 Wh or a volume energy density oflower than 180 Wh/l, it is not preferable to use the battery for aenergy storage system because the capacity is too low to be used for aenergy storage system and therefore it is necessary to increase thenumbers of batteries connected in series and in parallel, and moreoverit is difficult to compactly design the battery.

The thickness of the flat non-aqueous secondary battery of thisembodiment is preferably less than 12 mm, more preferably less than 10mm, and still more preferably less than 8 mm. For the lower limit of thethickness, 2 mm or more is practical when considering the packingefficiency of electrodes and the size of a battery (the area of thebattery surface increases as the thickness thereof decreases in order toobtain the same capacity). When the thickness of the battery becomes 12mm or more, it is difficult to sufficiently release the heat produced inthe battery to the outside or the temperature difference between theinner portion and the vicinity of the surface of the battery increasesand the internal resistance differs and resultantly, fluctuations ofcharge capacity and voltage in the battery increase. Though a specificthickness is properly determined in accordance with the battery capacityand energy density, it is preferable to design the battery at a maximumthickness at which an expected radiation of heat is obtained.

It is possible to form the front and back surfaces of the flatnon-aqueous secondary battery of this embodiment into various shapessuch as angular shape, circular shape, and elliptic shape, etc. Thetypical angular shape is rectangle. However, it is also possible to formthe front and back surfaces into a polygon such as a triangle orhexagon. Moreover, it is possible to form the battery into a cylindricalshape having a small thickness. In the case of the cylindrical shape,the thickness of the cylinder corresponds the thickness of a batterydescribed above. From the viewpoint of easiness of manufacture, it ispreferable that the front and back surfaces of the flat shape batteryare rectangular and the battery is the notebook type as shown in FIG. 1.

Next, a method for manufacturing a notebook-shaped battery case isdescribed regarding a method for manufacturing a battery case comprisingthe upper case 1 and the bottom case 2. In general, a household smallprismatic battery is approximately 50 mm square and has a thickness ofapprox. 6 mm. As shown in FIG. 3, the battery case is manufactured bylaser-welding a bottom case 21 (also serving as a negative terminal) anda upper case 22. The bottom case 21 is formed by deep-drawing of a thickplate. The upper case 22 is provided with a safety vent and a positiveterminal.

However, it is difficult to manufacture the notebook-type battery shownin FIG. 1 by the method same as the case of a small secondary battery.That is, the bottom case 2 of the battery case is obtained by bending athin plate having the shape shown in FIG. 4 inward along the broken lineL1 and further bending it outward along the alternate long and shortdash line L2, thereafter welding the corner shown by A or drawing a thinplate (very shallow drawing), and welding the upper case 1 on which aterminal and a safety vent are set as shown in FIG. 1. Alternatively,the battery case can be manufactured by bending a thin plate and weldingthe portion A as shown in FIG. 5 to form a structure 13 and furtherwelding lateral lids 11 and 12 to the a structure 13.

A material for a battery case such as the above thin plate is properlyselected in accordance with the purpose or shape of a battery. Iron,stainless steel, or aluminum is generally and practically used thoughnot limited specifically. The thickness of a battery case is properlydetermined in accordance with the purpose, shape, or material of thebattery case though not limited specifically. Preferably, the thicknessof the portion of 80% or more of the surface area of a battery(thickness of the portion having the largest area constituting a batterycase) is 0.2 mm or more. If the above thickness is less than 0.2 mm, itis not preferable because a strength required to manufacture a batterycannot be obtained. From this point of view, a thickness of 0.3 mm ormore is more preferable. Moreover, it is preferable that the thicknessof the above portion is 1 mm or less. A thickness of more than 1 mm isnot preferable because the internal volume of the battery decreases andthereby, a sufficient capacity cannot be obtained or the weightincreases. From this point of view, it is more preferable that thethickness is 0.7 mm or less.

As described above, by designing the thickness of a non-aqueoussecondary battery to less than 12 mm, when the battery has a largecapacity of e.g. 30 Wh or more and a high energy density of e.g. 180Wh/l, rise of the battery temperature is small even under high-ratecharge/discharge and the battery can have a superior heat radiationcharacteristic. Therefore, heat storage of the battery due to internalheat is reduced, and resultantly it is possible to prevent thermalrunaway of a battery and provide a non-aqueous secondary batterysuperior in reliability and safety.

A positive-electrode active material of a non-aqueous secondary batteryof the present invention is not limited as long as the material is apositive-electrode material for lithium batteries. It is possible to useone of lithium-containing cobalt-based oxides, lithium-containingnickel-based oxides, and lithium-containing manganese-based oxides, or amixture of these substances, or moreover a compound material obtained byadding at least one different-type metal element to these compoundoxides. These materials are preferably used to realize a high-voltagelarge-capacity battery. From the view point of safety, it is preferableto use manganese oxide having a high thermal-decomposition temperature.As the manganese oxide, the following are listed: lithium-containingmanganese oxides such as LiMn₂O₄, a compound material obtained by addingat least one different-type metal element to these compound oxides, andLiMn₂O₄ containing lithium and oxygen more than the theoretical ratio.

A negative-electrode active material of a non-aqueous secondary batteryof the present invention is not limited as long as the material is anegative-electrode material for lithium batteries. A material that canbe doped or undoped with lithium is preferable because reliability suchas safety or cycle life is improved. As materials which can be doped orundoped with lithium, the following can be used: graphite materials,carbon-based material, metal oxide such as tin-oxide-based material orsilicon-oxide-based material which are used as negative-electrodematerials of publicly-known lithium ion batteries, and an electricallyconducting polymer represented by a polyacenic semiconductors.Particularly, from the viewpoint of safety, it is preferable to use apolyacenic substance producing small heat at approximately 150 degreeCelsius or a material containing the polyacenic substance.

As the electrolyte of a non-aqueous secondary battery of the presentinvention, it is possible to use a non-aqueous electrolyte containingpublicly-known lithium salt and the electrolyte is properly selected inaccordance with the condition such as the sort of a positive-electrodematerial or negative-electrode material or charge voltage. Morespecifically, a material is used which is obtained by dissolving lithiumsalt such as LiPF₆, LiBF₄, or LiClO₄ in one of propylene carbonate,ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethylcarbonate, dimethoxyethane, g-butyrolactone, methyl acetate, and methylformate, or an organic solvent such as a mixed solvent of two types ofthese substances or more. Further, it is possible to use a gel or solidelectrolyte.

Though the concentration of an electrolyte is not limited, 0.5 mol/l to2 mol/l are generally practical. It is preferable to use the electrolytehaving a moisture of 100 ppm or less.

The word non-aqueous electrolyte referred to in the description andclaims of this application denotes either of non-aqueous electrolyte ororganic electrolyte, and either of gel or solid electrolyte.

Embodiments of a secondary battery (flat non-aqueous secondary batteryhaving an energy capacity of 30 Wh or more and a volume energy densityof 180 Wh/l or more and a thickness of less than 12 mm) of the presentinvention are shown and further specifically described below.

Embodiment 1-1

A secondary battery of an embodiment of the present invention wasconstituted as described below.

(1) A mixture slurry for a positive-electrode was obtained by mixing 100parts by weight of spinel-type LiMn₂O₄ (made by SEIMI CHEMICAL; productNo. M063), 10 parts by weight of acetylene black, and 5 parts by weightof polyvinylidene fluoride (PVdF) with 100 parts by weight ofN-methylpyrrolidone (NMP). The slurry was applied to the both sides ofan aluminum foil having a thickness of 20 μm and dried and then, pressedto obtain a positive electrode. FIG. 6 is an illustration of anelectrode. In the case of this embodiment, the coating area (W1×W2) ofan electrode (101) is 268×178 mm2 and slurry is applied to the bothsides of a 20 μm aluminum foil (102) at a thickness of 120 μm. As aresult, the electrode thickness t is 260 μm. One of the edge portions ofthe current collector extending along the arrow W2 and having a width of1 cm is not coated with the electrode, and a tab 103 (aluminum having athickness of 0.1 mm and a width of 6 mm) is welded thereto.

(2) A mixture slurry for a negative-electrode was obtained by mixing 100parts by weight of graphitized mesocarbon microbeads (MCMB: made byOSAKA GAS CHEMICAL Co., Ltd.; product No. 6 28) and 10 parts by weightof PVdF with 90 parts by weight of NMP. The slurry was applied to theboth sides of a copper foil having a thickness of 14 μm and dried, andthen pressed to obtain a negative electrode. Because the shape of thenegative electrode is the same as the above positive electrode, thenegative electrode is described by referring to FIG. 6. In the case ofthis embodiment, the coating area (W1×W2) of the electrode (101) is270×180 mm2 and the slurry is applied to both sides of the copper foil(102) at a thickness of 80 μm. As a result, the electrode thickness t is174 μm. One of the edge portions of the current collector extendingalong the arrow W2 and having a width of 1 cm is not coated with theelectrode, and a tab 103 (nickel having a thickness of 0.1 mm and awidth of 6 mm) is welded thereto.

Moreover, the slurry was applied to only one side by the same method anda single-sided electrode having a thickness of 94 μm was formed by thesame method except for the application of the slurry. The single-sidedelectrode is positioned at the outermost side in the stacked electrodeswhich is described in the following Item (3) (101 c in FIG. 6).

(3) Ten positive electrodes and eleven negative electrodes (including 2single-sided electrodes) obtained in the above Item (1) were alternatelystacked with a separator 104 (made by TONEN TAPIRUSU Co., Ltd.; made ofporous polyethylene) held between each of the layers to form anelectrode-stacked body.

(4) The battery bottom case (designated as 2 in FIG. 1) was formed bybending a thin plate made of SUS304 having the shape shown in FIG. 4 anda thickness of 0.5 mm inward at the lines L1 and outward at the lines L2and then arc-welding the corners A. The upper case (designated as 1 inFIG. 1) of the battery case was also formed with a thin plate made ofSUS304 having a thickness of 0.5 mm. Terminals 3 and 4 (diameter of 6mm) made of SUS304 and a safety-vent hole (diameter of 8 mm) are formedon the upper case 1. The terminals 3 and 4 are insulated from the uppercase 1 by a packing made of polypropylene.

(5) Each positive terminal 103 a of the electrode-stacked body made inthe above Item (3) was welded to the tab 3 and each negative terminal103 b was welded to the tab 4 through a connection line and then, theelectrode-stacked body was set to the battery bottom case 2 and fixed byan insulating tape to laser-weld the overall circumference along theedge A in FIG. 1. Thereafter, a solution was made by dissolving LiPF6 ata concentration of 1 mol/l in a solvent obtained by mixing ethylenecarbonate and diethyl carbonate at a weight ratio of 1:1. The solutionwas poured through a safety-vent hole as an electrolyte and the hole wasclosed with aluminum foil having a thickness of 0.1 mm.

(6) The formed battery had a size of 300×210 mm2 and a thickness of 6mm. The battery was charged by a constant-current/constant-voltagecharging for 18 hours, in which the battery was charged up to 4.3 V by acurrent of 3 A and then charged by a constant voltage of 4.3 V. Then,the battery was discharged to 2.0 V by a constant current of 30 A. Thedischarged capacity was 26 Ah, energy capacity was 91 Wh, and volumeenergy density was 240 Wh/l.

(7) As a result of charging and discharging the battery in athermostatic chamber at 20 degree Celsius by the method described in theabove Item (6), a rise of the battery temperature was hardly observedafter the end of discharge.

COMPARATIVE EXAMPLE 1-1

(1) A battery was constituted similarly to the case of the aboveembodiment except for changing electrode sizes, numbers of electrodes tobe stacked, and battery sizes. In the following list, the electrode sizedenotes the size of the negative electrode. The size of the positiveelectrode is 2 mm smaller than the negative electrode size in each side.The number of electrodes to be stacked denotes the number of positiveelectrodes. The number of negative electrodes is one more than thenumber of positive electrodes as described for the embodiment 1-1, inwhich two single-side-coated electrodes are included.

An energy capacity was measured by the same method as Item (6) of theembodiment. As a result of performing discharge by the same method asItem (7) of the embodiment and measuring the surface temperature of thebattery, discharge was stopped for safety because the temperature wasgreatly raised during the discharge.

-   -   Electrode size (W1×W2): 110×170 (mm)    -   Number of electrodes to be stacked: 26    -   Battery size: 140×200×140 (mm)    -   Energy capacity: 85 (Wh)    -   Energy density: 217 (Wh/l)

Even in the case of the embodiment battery having a battery energycapacity of approximately 90 Wh, the battery surface temperature hardlyrose when the battery thickness was less than 12 mm. However, thecomparative example having a thickness of 14 mm showed a highsurface-temperature rise. Therefore, it is clear that theorganic-electrolyte battery of the present invention shows a smalltemperature rise even if the battery is quickly discharged and has ahigh safety.

[Preferable Negative Electrode Used for Secondary Battery of the PresentInvention]

In general, lithium-containing manganese oxide used for a non-aqueoussecondary battery is a positive-electrode material suitable for a largescale battery. It is reported that a high-safety battery is obtained byusing the lithium manganese oxide for a positive electrode compared withlithium cobalt oxide and lithium-containing nickel oxide (Like Xie etal., Mat. Res. Soc. Symp. Proc., Vol. 393, 1995, pp. 285-304). Thepositive-electrode material has a density and a capacity lower thanthose of lithium-containing cobalt-based oxide and lithium-containingnickel oxide. Therefore, to obtain a large-capacity battery, it ispreferable to use A, B, or C-type negative electrodes described belowand thereby improved safety is also expected.

(A-Type Negative Electrode)

In the case of preferable graphite to be used for the negativeelectrodes 101 b and 101 c as a negative-electrode active material, the(d002) spacing of (002) planes measured by the X-ray wide-anglediffraction method is normally 0.34 nm or less, preferably 0.3354 to0.3380 nm, or more preferably 0.3354 to 0.3360 nm. When the planespacing (d002) exceeds 0.34 nm, crystallinity lowers. Therefore, thechange of potentials due to discharge of lithium ions increases and theeffective capacity usable as a battery lowers.

The following are listed as materials for manufacturing the abovegraphites: cokes such as pitch coke and needle coke, polymers, andcarbon fibers. By baking these materials at a temperature of 1,500 to3,000 degree Celsius in accordance with the conventional method, it ispossible to obtain desired graphite materials. Specifically, graphiteincludes mesophase-pitch-based graphite fiber, graphitized mesocarbonmicrobeads (hereafter referred to as graphitized MCMB),vapor-phase-epitaxial carbon fiber, and graphite whisker. Particularly,because the particles of graphitized MCMB are almost spherical, ahigh-density electrode to be mentioned later can be easily obtained.

The particle diameter of the above graphite is preferably 1 to 50 μm,more preferably 3 to 40 μm, or still more preferably 5 to 35 μm. If theparticle diameter is less than 1 μm, it is impossible to raise theelectrode density. However, if the particle diameter exceeds 50 μm, alarge capacity cannot be obtained because the graphite is broken when anelectrode having a small thickness of approximately 100 μm is pressed toraise the electrode density.

The negative electrodes 101 b and 101 c are obtained, for example, byusing an organic solvent solution of a resin serving as a binder,applying the above graphite onto a metal member serving as a currentcollector, drying the metal member and pressing it if necessary. Whenusing a resin as a binder, a negative electrode is obtained which isstable even at a high temperature and has a high adhesiveness with ametal member serving as a current collector.

The negative electrodes 101 b and 101 c thus obtained and having aporosity of 20 to 35% and an electrode density of 1.40 to 1.70 g/cm³(more preferably having an electrode density of 1.45 to 1.65 g/cm³,particularly preferably having an electrode density of 1.50 to 1.65g/cm³) are easily impregnated with the electrolyte, in which lithiumions and electrons are smoothly moved. Therefore, it is possible toobtain a negative electrode having a high capacity of electrode of 400mAh/cm³ or more. By using a negative electrode having a high capacity ofelectrode of 400 mAh/cm³ or more, it is possible to improve the batterycapacity without raising the utilization ratio of a negative-electrodeactive material and thus the safety such as prevention of lithium fromelectrodeposition or the like can be easily secured.

The above resin serving as a binder binds graphite particles each otherand fixes active-material particles on metallic foil. As the binderresin, the following materials can be used without limitation thereto:fluorinated resins such as polyvinylidene fluoride (PVdF) andpoly-4-ethylene fluoride, fluorine rubber, SBR, acrylic resin, andpolyolefins such as polyethylene and polypropylene. Among them, a resinsoluble in widely used organic solvents (such as N-methylpyrrolidone,toluene, and styrene) and superior in electrolyte resistance andwithstanding high-voltage are preferable, and particularlypolyvinylidene fluoride (PVdF) is preferable.

A binder mixing quantity in a negative electrode is not limited. It isallowed to properly determine the binder mixing quantity in accordancewith the type, particle diameter, shape, or thickness and strength of apurposed electrode. However, it is normally preferable to set the bindermixing quantity in a range of 1 to 30% of the weight of graphite.

In this embodiment, as a metal for the current collector copper foil,stainless-steel foil, or titanium foil can be used without limitationthereto. Moreover, it is possible to use materials allowing an electrodeto be formed on metallic foil or between metallic materials, such asexpand metal or mesh material. Among these materials, it is morepreferable to use a copper foil having a thickness of 1 to 50 μm becauseit allows a negative electrode to be easily formed by a coating methodto be mentioned later and is superior in strength and electricresistance.

A method of using polyvinylidene fluoride (PVdF) as a binder resin and acopper foil as a current collector is described below as a specificmethod for manufacturing the negative electrode for a non-aqueoussecondary battery of this embodiment having a high capacity of electrodeof 400 mAh/cm³. It is needless to say that methods for manufacturing thenegative electrode of this embodiment are not limited to the method.

First, a slurry is prepared by uniformly dissolving graphite in abinder-resin solution obtained by dissolving polyvinylidene fluoride(PVdF) in N-methylpyrrolidone. In this case, it is also possible to adda conductive material such as acetylene black or binder assistant suchas polyvinyl pyrrolidone. Then, the obtained slurry is applied ontocopper foil by a coater and dried, and an electrode layer is formed onthe copper foil, and then pressed to obtain a negative electrode for thenon-aqueous secondary battery, which has a thickness of 50 to 500 μm.The electrode layer is formed on both sides or either side of the copperfoil according to necessity.

The negative electrode thus obtained is a high-density electrode whosecapacity is hardly lowered and having a density of 1.40 to 1.70 g/cm³,preferably having a density of 1.45 to 1.65 g/cm³, or more preferablyhaving a density of 1.50 to 1.65 g/cm³, a porosity of 20 to 35%, and ancapacity of electrode of 400 mAh/cm³ or more. The density and porosityare values of an electrode layer formed on metallic foil, which can becalculated in accordance with the true densities of the graphite andbinder resin in the electrode layers and the electrode density. Thecapacity of electrode is a capacity expressed on the basis of the volumeof electrode layers.

(B-Type Negative Electrode)

A graphite-based particle used for the negative electrodes 101 b and 101c as a negative-electrode active material has a double structureobtained by covering the surface of a graphite particle with amorphouscarbon. By using the double-structure graphite-based particle,deterioration of charge rate probably due to decomposition ofelectrolyte is substantially prevented and a graphite structure isprevented from breaking.

In the negative electrodes 101 b and 101 c, the (d002) spacing of (002)planes of a graphite-based particle used as an active material isnormally 0.34 nm or less, more preferably 0.3354 to 0.3380 nm, and stillmore preferably 0.3354 to 0.3360 nm as measured by the X-ray wide-anglediffraction method. When the plane interval exceeds 0.34 nm,crystallinity lowers and thereby, the change of potentials due todischarge of lithium ions increases and the effective capacity usable asa battery lowers.

The plane spacing of amorphous carbon layers coating the graphite-basedparticles is such that the (d002) spacing of (002) planes is 0.34 nm ormore, preferably about 0.34 to 0.38 nm, more preferably about 0.34 to0.36 nm as measured by the X-ray wide-angle diffraction method. Whenthis value is below 0.34 nm, crystallinity is too large, and thereby,charging rate lowers probably due to decomposition of electrolyte, andcarbon material is broken due to increase/decrease of the plane distancewith repeated charging and discharging. On the other hand, when thisvalue exceeds 0.38, the displacement of lithium ions is restricted andthus the effective capacity usable as a battery lowers.

Materials for manufacturing the above graphite-based particles includecokes such as pitch coke and needle coke, polymers, and carbon fibers.By baking these materials in accordance with the conventional method ata temperature of 1,500 degree Celsius to 3,000 degree Celsius, desiredgraphite-based particles can be obtained.

As materials for forming a covering layer of graphite particle, organicmaterials such as pitches and polymers can be used. Amorphous carbon forthe covering layer can be obtained by covering the surface of thegraphite-based particle material obtained in accordance with the abovemethod with a liquid organic material (such as melted pitch) and bakingthe covering organic material at a temperature of 500 degree Celsius to2,000 degree Celsius to carbonize it.

Furthermore, the above double-structure graphite-based particles have ahigh capacity per weight of 350 mAh/g and achieve a high initialefficiency of 90% or more. Therefore, it is possible to improve thebattery capacity without raising the utilization ratio of anegative-electrode active material and thereby, the safety such asprevention of lithium from electrodeposition can be easily secured.

The diameter of a double-structure active-material particle comprisingthe above graphite-based particle and its covering layer is preferably 1to 50 μm, more preferably 3 to 40 μm, and still more preferably 5 to 35μm. When the particle diameter of the double-structure body is less than1 μm, it is impossible to improve the electrode density. When theparticle diameter exceeds 50 μm, a large capacity cannot be obtainedbecause a double-structure active-material particle is broken when anelectrode having a small thickness of 100 μm is pressed to raise anelectrode density.

The negative electrodes 101 b and 101 c are obtained by using an organicsolvent solution of a resin serving as a binder, thereby applying theabove double-structure active-material particles onto a metal serving asa current collector, drying them, and pressing them if necessary. Whenusing a resin as a binder, a negative electrode is obtained which isstable even at a high temperature and has high adhesiveness with a metalmember serving as a current collector.

The negative electrodes 101 b and 101 c obtained as described above andhaving a porosity of 20 to 35%, an electrode density of 1.20 to 1.60g/cm³ (more preferably having a porosity of 1.35 to 1.60 g/cm³ orparticularly preferably having a porosity of 1.40 to 1.60 g/cm³) areeasily impregnated with electrolyte, in which lithium ions and electronsare smoothly moved. Therefore, it is possible to obtain a negativeelectrode having a high capacity of electrode of 400 mAh/cm³ or more. Anegative electrode having a high capacity of electrode of 400 mAh/cm³ ormore is more effective used in view of the capacity and safety of abattery as described below.

The above resin serving as a binder binds double-structureactive-material particles each other and fixes active-material particleson the metallic foil. As binder resins the following materials can beused without limitation thereto: fluorinated resins such aspolyvinylidene fluoride (PVdF) and poly-4-ethylene fluoride, fluorinerubber, SBR, acrylic resin, and polyolefins such as polyethylene orpolypropylene. Among them, a resin soluble in widely used organicsolvents (such as N-methylpyrrolidone, toluene, and styrene) andsuperior in electrolyte resistance and withstanding high-voltage ispreferable, and particularly polyvinylidene fluoride (PVdF) ispreferable.

A binder mixing quantity in a negative electrode is not limited. It isallowed to properly determine the binder mixing quantity in accordancewith the type, particle diameter, shape, or thickness and strength of apurposed electrode. However, it is normally preferable to set the bindermixing quantity in a range of 1 to 30% of the weight of active-materialparticles.

In this embodiment, as a metal for current collector a copper foil,stainless-steel foil, or titanium foil can be used without limitationthereto. Moreover, it is possible to use materials allowing an electrodeto be formed on a metallic foil or between metallic materials, such asexpand metal or steel. Among these materials, it is more preferable touse a copper foil having a thickness of 1 to 50 μm because it allows anegative electrode to be easily formed by a coating method to bementioned later and is superior in strength and electric resistance.

A method of using polyvinylidene fluoride (PVdF) as a binder resin and acopper foil as a current collector is described below as a specificmethod for manufacturing the negative electrode for a non-aqueoussecondary battery of this embodiment having a high capacity of electrodeof 400 mAh/cm³. It is needless to say that methods for manufacturing thenegative electrode of this embodiment are not limited to the abovemethod.

First, a slurry is prepared by uniformly dissolving double-structureactive-material particles in a binder-resin solution obtained bydissolving polyvinylidene fluoride (PVdF) in N-methylpyrrolidone. Inthis case, it is also possible to add a conductive material such asacetylene black or binder assistant such as polyvinyl pyrrolidone. Then,the obtained slurry is applied onto a copper foil by a coater and dried,and an electrode layer is formed on the copper foil, and then pressed toobtain a negative electrode for the non-aqueous secondary battery, whichhas a thickness of 50 to 500 μm. The electrode layer is formed on bothsides or either side of the copper foil according to necessity.

To manufacture a negative electrode, it is necessary to prevent graphitefrom breaking. For example, in the case of the above manufacturingexample, it is necessary to pay attention to various conditions in thepressing step. Specifically, the following can be listed as theseconditions: a pressing rate, tension, and roller curvature for pressingan electrode layer formed on a metallic foil by rollers, a dried state(remaining amount of solvent) of the electrode layer before pressing,and a pressing temperature.

It is desirable to control a dried level (remaining amount of solvent)of an electrode layer before pressed normally at 1 to 10%, preferably at1 to 8%, and still more preferably at 2 to 5%. When these amounts ofsolvent remain, it is possible to improve an electrode-layer density bypressing without breaking graphite. That is, when a certain amount ofsolvent remains, the solvent is present on surfaces of graphite, binder,and conductive material, which supposedly improves slippage betweenthese materials during the pressing step and resultantly anelectrode-layer density can be improved without breaking graphitematerial.

In the conventional common sense, a solvent is regarded as an impurityand it has been considered that a remaining amount of the solvent shouldbe minimized (a remaining amount of the solvent should be kept at 0.2%or less). However, according to the study of the present inventor, whencontrolling a remaining amount of solvent within a predetermined range,negative electrode for a non-aqueous secondary battery having a highelectrode density and a large capacity can be obtained compared with thecase of a conventional method.

An electrode-layer pressing temperature is normally kept at ordinarytemperature (25 degree Celsius) to 140 degree Celsius, preferably keptat ordinary temperature to 100 degree Celsius, or more preferably keptat ordinary temperature to 70 degree Celsius.

By previously adjusting the above conditions (particularly, a remainingamount of a solvent) on trial, it is possible to manufacture anelectrode without breaking graphite, that is, an electrode can bemanufactured without lowering the capacity even if the density of theelectrode is raised.

The negative electrode thus obtained is a high-density electrode whosecapacity is hardly lowered and having a density of 1.20 to 1.60 g/cm³,preferably having a density of 1.35 to 1.60 g/cm³, or more preferablyhaving a density of 1.40 to 1.50 g/cm³, a porosity of 20 to 35%, and ancapacity of electrode of 400 mAh/cm³ or more. The density and porosityare values of an electrode formed on metallic foil, which can becalculated in accordance with true densities of double-structureactive-material particles and a binder resin and the electrode densityin the electrode layer. Also, the capacity of electrode is a capacityexpressed on the basis of the volume of electrode layers.

(C-Type Negative Electrode)

The negative-electrode active material used for the negative electrodes101 b and 101 c can be manufactured using carbon (hereafter referred toas “coating graphite”) which is obtained by mixing at least either ofartificial graphite or natural graphite with carbon having a volatilecomponent on the surface and/or inside thereof (hereafter referred to as“volatile-component-contained carbon”) and then baking them. The activematerial thus manufactured is substantially prevented from deteriorationof the charge rate probably due to decomposition of electrolyte does notsubstantially occur and a graphite structure is also prevented frombreaking.

The coating graphite has a structure in which a volatile componentderived from a volatile-component-contained carbon attaches at least apart of artificial graphite and/or natural graphite by baking a mixedmaterial or covers at least a part of artificial graphite and/or naturalgraphite. It is presumed that the above attaching structure or coveringstructure is formed when the volatile component of thevolatile-component-contained carbon once vaporizes and then attaches apart or the whole of the artificial graphite and/or natural graphite orcovers a part or the whole of the artificial graphite and/or naturalgraphite. In other words, it is presumed that a part or the whole of theartificial graphite and/or natural graphite is covered in a gaseousphase.

In general, artificial graphite and natural graphite serving asnegative-electrode materials have a problem of damaging the stability ofthe electrolyte because they respectively have a large specific surfacearea though they respectively have a large capacity usable as a battery.However, to cover artificial graphite or natural graphite in a gaseousphase, it is presumed that the covering thickness is very small anduniform. As a result, it is possible to substantially decrease thespecific surface area of artificial graphite or natural graphite withoutsubstantially lowering a large capacity of the artificial graphite ornatural graphite and therefore, it is presumed that high-capacitycoating graphite can be obtained.

It is possible to form coating graphite in a liquid phase. That is, bysoaking graphite serving as a core material in liquid-phase “carbon forforming a coat”, it is possible to obtain coating graphite. Also in thiscase, by decreasing a ratio of [coat-forming volatile component]/[corematerial+coat-forming volatile component] (this ratio is hereafterreferred to as “coating ratio”), it is expected that higher-capacitycarbon may be obtained similarly to the case of the gaseous phase.Actually, however, forming a thin covering layer in a liquid phage isnot suitable, because a problem occurs that the covering layer isseparated from a core material or the covering layer is lacking inuniformity and the specific surface area of coating graphite increases.

As volatile-component-contained carbon used for this embodiment, thefollowing can be listed: carbon (volatile-component-contained carbon)serving as a core material a part or the whole of which is covered withcoat-forming volatile component (such as coal tar pitch), mesocarbonmicro beads, carbon fiber, mesophase pitch, isotropic pitch, resin, anda mixture of these materials. Among them, thevolatile-component-contained carbon is preferable from the viewpoint ofcost. It is preferable that the coating ratio of thevolatile-component-contained carbon is 0.01 or more, it is morepreferable that the ratio is 0.05 or more, or it is still morepreferable that the ratio is not less than 0.05 and not more than 0.3.

If the coating ratio of the volatile-component-contained carbon is toolow, the carbon does not sufficiently cover or attach a part or thewhole of artificial graphite and/or natural graphite because the amountof a volatile component to be evaporated is small when the material isbaked while mixed with artificial graphite and/or natural graphite.However, if the coating ratio is too large, it is difficult to obtain asufficient capacity because the capacity of a low-potential portiondepending on a core material lowers when a battery is manufactured. Theamount of the “volatile component” was determined by the following: Acarbon component derived from heavy oil covering the circumference ofcarbon serving as a core material was solvent-analyzed in accordancewith the method specified in JIS K2423. Firstly, a quinoline component(%) was measured and then {100-(quinoline component)} was defined as aquinoline soluble component(%). The quinoline soluble component is theabove “amount of coat-forming volatile component” and the above “coatingratio” can be calculated by using the amount of coat-forming volatilecomponent and the carbon serving as a core material.

Volatile-component-contained carbon in which a part or the whole ofcarbon serving as a core material is covered with a volatile componentis manufactured as described below. That is, carbon particles serving asa core material is soaked in coal-based or oil-based heavy oil such astar or pitch preferably at 10 to 300 degree Celsius to separate thecarbon from the heavy oil, and then an organic solvent is added to theseparated carbon to clean them preferably at 10 to 300 degree Celsius.By properly adjusting the mixed ratio between the carbon particles andthe heavy oil, it is possible to omit the above cleaning step. However,it is preferable to execute the cleaning step. When omitting thecleaning step, a problem may occur that particles of thevolatile-component-contained carbon adhere or cohere each other whenbaked or the volatile component does not uniformly attach or cover thecore material. Moreover, when manufacturing volatile-component-containedcarbon while soaking carbon in heavy oil at a temperature exceeding 300degree Celsius and accelerating the polycondensation of heavy oil, thesame problem may occur. Furthermore, it is possible to perform thebaking step at 300 to 600 degree Celsius instead of the above cleaningstep. In this case, however, volatile-component-contained carbon doesnot uniformly attach or cover a core material though particles do noteasily adhere or cohere each other.

To manufacture volatile-component-contained carbon, a mechanicalstirring method using a nauta mixer, ribbon mixer, screw-type kneader,or widely used mixer is used as a method for mixing carbon particleswith heavy oil.

Though the mixing ratio between artificial graphite and/or naturalgraphite and volatile-component-contained carbon mainly depends on theamount of the volatile component of the carbon, it is normally 10 to1,000 parts by weight of artificial graphite and/or natural graphite,more preferably 10 to 300 parts by weight of artificial graphite and/ornatural graphite, still more preferably 30 to 100 parts by weight ofartificial graphite and/or natural graphite, to 100 parts by weight ofthe volatile-component-contained carbon. When the amount of artificialgraphite and/or natural graphite is too small, the ratio of thecoating-graphite component that should serve as a higher capacity partin carbon for a battery lowers and thereby, the capacity is notsufficiently raised. However, when the amount of artificial graphiteand/or natural graphite is too large, the amount of a volatile componentto be evaporated when baking a mixture relatively decreases. Therefore,artificial graphite and/or natural graphite is not sufficiently coveredand a desired specific surface area of carbon increases.

A mixture of artificial graphite and/or natural graphite andvolatile-component-contained carbon is baked in a reducing atmosphere orinert gas flow, or a non-oxidation atmosphere such as a closed statecontaining an inert gas or vacuum state. Because the mixture is baked inorder to cover a part or the whole of artificial graphite and/or naturalgraphite by evaporating a volatile component in multilayer carbon in agaseous phase, it is more preferable to bake the mixture in anatmosphere in which the volatile component ofvolatile-component-contained carbon easily stays, that is, in a reducingatmosphere or inert-gas contained state. Carbonization in a vacuum statehas an effect of removing a surface functional group of carbon and anadvantage that retention can be reduced but has a disadvantage that avolatile component is easily lost from the volatile-component-containedcarbon.

The above mixture is baked to be carbonized normally at a temperature ofabout 600 degree Celsius to 2,000 degree Celsius, and more preferably ata temperature of 900 degree Celsius to 1,300 degree Celsius. The abovemixture is baked to be graphitized normally at a temperature of about2,000 degree Celsius to 3,000 degree Celsius, more preferably at atemperature of about 2,500 degree Celsius to 3,000 degree Celsius. Anungraphitized part may remain in a baked product depending on a mixturebaking condition and the remaining ungraphitized part may slightlyinfluence the characteristic of a negative electrode. However, this doesnot substantially matter. However, to further improve thenegative-electrode characteristics, it is more preferable to usegraphite as a core material of volatile-component-contained carbon orfurther improve the graphitization degree of a baked product by bakingat a higher temperature.

It is possible to select a temperature-rise rate when baking a mixturefrom a range of 1 to 300 degree Celsius/hr at any baking temperature.The baking time ranges between 6 hours and one month.

The particle diameter of coating graphite used as a negative-electrodeactive material in this embodiment is normally 1 to 50 μm, morepreferably 3 to 40 μm, and still more preferably 5 to 35 μm. When theparticle diameter of the coating graphite is too small, it is impossibleto raise an electrode density. However, when the particle diameter istoo large, a large capacity is not obtained because covering-graphiteparticles are broken when performing pressing to raise an electrodedensity in order to manufacture a thin electrode having a thickness ofapproximately 100 μm.

The negative electrodes 101 b and 101 c are obtained by using an organicsolvent solution of a resin serving as a binder, applying thecoating-graphite particles onto a metal member serving as a currentcollector, drying them, and pressing them if necessary. When using aresin as a binder, a negative electrode is obtained which is stable evenat a high temperature and has a high adhesiveness with a metal memberserving as a current collector.

The negative electrodes 101 b and 101 c thus obtained and having adensity of 1.20 to 1.60 g/cm³ (more preferably having a density of 1.35to 1.60 g/cm³) and a porosity of 20 to 35% are easily impregnated withelectrolyte, in which lithium ions and electrons are smoothly moved.Therefore, it is possible to obtain a negative electrode having a highcapacity of electrode of 400 mAh/cm³ or more. Use of the negativeelectrode having a high capacity of electrode of 400 mAhl/cm³ or more ismore effective for the battery capacity and safety described below.

The above resin serving as a binder binds coating-graphite particleseach other and binds and fixes active-material particles onto metallicfoil. As resins serving as binders the following can be used withoutlimitation thereto: fluorinated resins such as polyvinylidene fluoride(PVdF) and poly-4-ethylene fluoride, fluorine rubber, SBR, acrylicresin, and polyolefins such as polyethylene and polypropylene. Amongthese materials, a material is preferable which is particularly solublein organic solvents for general purposes (such as N-methylpyrrolidone,toluene, and styrene) and superior in electrolyte resistance andwithstanding a high-voltage. For example, polyvinylidene fluoride (PVdF)is preferable.

A binder mixing quantity is not limited. It is allowed to properlydetermine a binder mixing quantity for a negative electrode inaccordance with the type, particle diameter, shape, purposed electrodethickness, or strength of a coating-graphite particle. However, it isnormally preferable to use a rate of 1 to 30% of the weight ofactive-material particles.

In this embodiment, as a metal used as a current collector a copperfoil, stainless-steel foil, or titanium foil can be used withoutlimitation thereto. It is possible to use a metal allowing an electrodeto be formed on metallic foil or between metal materials such as expandmetal or steel. Among them, copper foil having a thickness of 1 to 50 μmis more preferable because the foil allows a negative electrode to beeasily manufactured in accordance with the coating method to bedescribed later and is superior in strength and electric resistance.

A method of using polyvinylidene fluoride (PVdF) as a binder resin andcopper foil as a current collector is described below as a specificmethod for manufacturing the negative electrode for a non-aqueoussecondary battery of this embodiment having a high capacity of electrodeof 400 mAh/cm³. It is needless to say that methods for manufacturing thenegative electrode of this embodiment are not limited to the abovemethod.

First, a slurry is prepared by uniformly dissolving coating graphite ina binder-resin solution obtained by dissolving polyvinylidene fluoride(PVdF) in N-methylpyrrolidone. In this stage, it is also possible to adda conductive material such as acetylene black or binder assistant suchas polyvinyl pyrrolidone. Then, the obtained slurry is applied ontocopper foil by a coater and dried, and an electrode layer is formed onthe copper foil, and then pressed to obtain a negative electrode havinga thickness of 50 to 500 μm for the non-aqueous secondary battery. Theelectrode layer is formed on both sides or either side of the copperfoil according to necessity.

The negative electrode thus obtained is a high-density electrode havinga density of 1.20 to 1.60 g/cm³ (more preferably having a density of1.35 to 1.60 g/cm³) and an capacity of electrode of 400 mAh/cm³ or more,but hardly lowering a capacity. The density and porosity are values ofan electrode layer formed on metallic foil, which can be calculated inaccordance with coating-graphite particles in an electrode and the truedensity of a binder resin, and an electrode density. The capacity ofelectrode is a capacity expressed on the basis of the volume ofelectrode layers.

When densities of A-, B, and C-type negative electrodes are too low, asufficient capacity of electrode cannot be obtained. However, when thedensities are too high, this is not preferable because a capacity islowered due to breakdown of graphite. When a porosity is too low, asufficient rate characteristic is not obtained. However, when theporosity is too high, a sufficient capacity of electrode is notobtained.

The above “capacity of electrode” is a capacity of an electrode definedby sufficiently doping and dedoping lithium. For example, the dedopingcapacity is measured by assembling electrochemical cells using a lithiummetal as an counter electrode and a reference electrode, incurring aconstant voltage to the counter electrode at a potential of 1 mV vs. thelithium-metal potential in a non-aqueous electrolyte to be mentionedlater, doping the lithium until a current value becomes small enough(e.g. 0.01 mA/cm²), then dedoping the lithium up to 2 V relative to thelithium potential at a sufficiently slow rate (e.g. 0.25 mA/cm²). Bydividing the dedoping capacity by an electrode volume, the capacity ofelectrode referred to in the present invention is obtained. Now, thedescription of each of the A, B, and C-type negative electrodes iscompleted.

The present invention is further specifically described below with thereference to an embodiment of each of the A, B, and C-type negativeelectrodes.

[A-Type Negative Electrode]

Embodiment 2- 1

(1) A positive-electrode mixture slurry was obtained by mixing 100 partsby weight of spinel-type LiMn₂O₄ (made by SEIMI CHEMICAL, product No.M063), 10 parts by weight of acetylene black, and 5 parts by weight ofpolyvinylidene fluoride (PVdF) with 100 parts by weight ofN-methylpyrrolidone (NMP). A positive electrode was obtained by applyingthe slurry to both sides of aluminum foil having a thickness of 20 μmand serving as a current collector, and by drying and pressing the foil.FIG. 6 is an illustration of an electrode. In the case of thisembodiment, the coating area (W1×W2) of an electrode 101 was 268×178 mm²and the slurry was applied to both sides of a current collector 102 of20 μm thickness at a thickness of 128 μm. As a result, the electrodethickness t was 276 μm. One of the edge portions of the shorter side ofthe current collector 102 was not coated in 1 cm width and a tab 103(aluminum with a thickness of 0.1 mm and a width of 6 mm) was welded.

(2) A negative-electrode slurry was obtained by mixing 100 parts byweight of graphitized mesocarbon microbeads (MCMB, made by OSAKA GASCHEMICAL, product No. 6-28) and 10 parts by weight of PVdF with 90 partsby weight of NMP. A negative electrode was obtained by applying theslurry to both sides of a copper foil having a thickness of 14 μm andserving as a current collector, and by drying and then pressing thefoil. Before pressing the foil, 4.3% of NMP was left in the electrode.The electrode density was 1.58 g/cm³, and previous evaluation of thecapacity of electrode of the electrode was 430 mAh/cm³. Because theshape of the electrode was the same as that of the above-describedpositive electrode, the negative electrode is described below withreference to FIG. 6. In the case of this embodiment, the coating area(W1×W2) of the electrode 101 was 270×180 mm² and the slurry was appliedto both sides of the current collector 102 of 14 μm thickness at athickness of 72 μm. As a result, the electrode thickness t was 158 μm.One of the edge portions of the shorter side of the current collector102 was not coated in 1 cm width and a tab 103 (nickel with a thicknessof 0.1 mm and a width of 6 mm) was welded.

The slurry was applied to only one side by the same method and asingle-sided electrode having a thickness of 86 μm was formed by thesame method except for the application of the slurry. The single-sidedelectrode was positioned at the outermost in the stacked electrodesdescribed in Item (3) (101 c in FIG. 2).

(3) An electrode-stacked body was formed by alternately stacking 10positive electrodes and 11 negative electrodes (including twosingle-sided electrodes) obtained in the above Item (1) with a separator104 (made by TONEN TAPIRUSU, porous polyethylene) held between each ofthe layers.

(4) The bottom case 2 of the battery (refer to FIG. 1) was formed bybending a thin plate made of SUS304 having the shape shown in FIG. 4 anda thickness of 0.5 mm inward along the broken lines L1 and moreoverbending the thin plate outward along the alternate long and short dashlines L2, thereafter arc-welding the corners A. The upper case 1 of thebattery was formed of a thin plate made of SUS304 having a thickness of0.5 mm. A positive electrode and a negative electrode 3 and 4 made ofSUS304 (diameter of 6 mm) and a safety-vent hole (diameter of 8 mm) wereformed on the upper case 1, and the positive and negative electrodes 3and 4 were insulated from the upper case 1 by a polypropylene packing.

(5) Each positive-electrode tab 103 a of the electrode-stacked body madein the above Item (3) was welded to the positive-electrode tab 3 andeach negative-electrode tab 103 b was welded to the negative-electrodetab 4 through a connection line and then, the electrode-stacked body wasset to the battery bottom case 2 and fixed by an insulating tape tolaser-weld the overall circumference along the edge A in FIG. 1.Thereafter, a solution made by dissolving LiPF₆ at a concentration of 1mol/l in a solvent obtained by mixing ethylene carbonate and diethylcarbonate at a weight ratio of 1:1 was poured through a safety-vent holeas electrolyte and the hole was closed by using an aluminum foil havinga thickness of 0.1 mm.

(6) The formed battery has a size of 300 mm×210 mm×6 mm. The battery wascharged by a constant-current/constant-voltage charging for 18 hours, inwhich the battery was charged up to 4.3 V by a current of 3 A and thencharged by a constant voltage of 4.3 V. Then, the battery was dischargedto 2.0 V by a constant current of 3 A. The discharge capacity was 27.5Ah, the energy capacity was 99 Wh, and the volume energy density was 262Wh/l.

(7) As a result of charging the battery and discharging the battery at acurrent of 30 A in a thermostatic chamber at 20 degree Celsius by themethod described in the above Item (6), rise of the battery temperatureat the end of discharge was small compared with the case of theassembled prismatic battery (thickness of 12 mm or more) having the samecapacity.

COMPARATIVE EXAMPLE 2-1 Comparison with Embodiment 2-1

A positive electrode was formed which was the same as that of theembodiment 2-1 except that slurry was applied to both sides of a currentcollector 102 at a thickness of 120 μm and the electrode thickness t wasset to 260 μm.

Then, a negative electrode was obtained by applying negative-electrodemixture slurry same as that of the embodiment 2-1 to both sides of thecurrent collector 102 in a condition different from that of theembodiment 2-1, drying the current collector 102, and then pressing it.Before pressing the current collector 102, 0.2% of NMP was left on theelectrode. The electrode density was 1.39 g/cm³ and the previousevaluation of the capacity of electrode of the electrode was 372mAh/cm³. In the case of the comparative example, the coating area(W1×W2) of an electrode 101 is 270×180 mm² and slurry was applied toboth sides of the current collector 102 of 14 μm thickness at athickness of 80 μm. As a result, the electrode thickness t was 174 μm.The only one side was coated in accordance with the same method and asingle-sided electrode of 94 μm thickness was formed by the same methodexcept for the single-sided coating. Other points were the same as thecase of the embodiment 2-1.

Thereafter, as a result of forming a battery in accordance with the samemethod as the case of the embodiment 2-1 and measuring the capacity, itshowed 25.8 Ah. The energy capacity was 93 Wh and the volume energydensity was 249 Wh/l that was lower than the case of the embodiment 2-1.

[B-Type Negative Eectrode]

(Formation of Electrode)

An electrode was formed by the following materials: double-structureactive-material particles used as a negative-electrode active materialand obtained by covering the surface of graphite particles withamorphous carbon, acetylene black (trade name: DENKA BLACK; made byDENKIKAGAKU KOGYOU Co., Ltd.) used as a conductive material, and asolution used as a binder and obtained by dissolving polyvinylidenefluoride (PVdF) (product name: KF#1100; made by Kureha Chemical IndustryCo., Ltd.) in N-methylpyrrolidone. That is, negative electrodes 1 to 7respectively having a thickness of 100 μm were formed by applying thepolyvinylidene fluoride (PVdF) solution to copper foil having athickness of 14 μm serving as a current collector and then, drying thefoil at 80 degree Celsius for 15 min, and continuously pressing the foilby a roller press having a radius of curvature of 30 cm while makingN-methylpyrrolidone remain.

An electrode 8 was formed similarly to the case of the electrode 1except for using graphitized MCMB (made by OSAKA GAS CHEMICAL Co., Ltd.;product No. 6-28).

Table 1 shows the diameters (mm) of the obtained double-structureactive-material particles and the (d002) spacing of (002) planes of thegraphite particles and its covering carbon layer measured by the X-raywide-angle diffraction method (unit is nm in both case). Table 2 showselectrode densities, initial capacities, and remaining amount of solventof the negative electrodes 1 to 8. Mixing ratios of electrode layers are90 wt % of graphite particles and 10 wt % of polyvinylidene fluoride(PVdF). TABLE 1 Double-structure Graphite particle Graphite Coveringcarbon material: No. diameter (μm) particle (d002) layer (d002) 1 10.335 0.340 2 1 0.335 0.380 3 1 0.337 0.340 4 20 0.335 0.360 5 20 0.3400.380 6 50 0.335 0.340 7 50 0.336 0.380

TABLE 2 Negative- Remaining Negative electrode Electrode Initial amountof electrode: active density capacity solvent No. material (g/cm³)(mAh/cm³) (wt %) 1 No. 1 1.40 435 2.1 2 No. 2 1.45 440 3.4 3 No. 3 1.53465 5.0 4 No. 4 1.60 468 10.0 5 No. 5 1.45 440 1.0 6 No. 6 1.42 438 4.87 No. 7 1.35 430 2.7 8 MCMB 1.39 370 2.5

As shown in Tables 1 and 2, the negative electrodes 1 to 7 usingdouble-structure active-material particles respectively have anelectrode density of 1.35 to 1.60 g/cm³ and a capacity of 400 mAh/cm³ ormore. Therefore, they respectively have a large capacity compared withthat of the electrode 8 using graphitized MCMB.

Embodiment 3-1

(1) A positive-electrode mixture slurry was obtained by mixing 100 partsby weight of spinel-type LiMn₂O₄ (made by SEIMI CHEMICAL; product No.M063), 10 parts by weight of acetylene black, and 5 parts by weight ofpolyvinylidene fluoride (PVdF) with 100 parts by weight ofN-methylpyrrolidone (NMP). A positive electrode was obtained by applyingthe slurry to both sides of an aluminum foil having a thickness of 20 μmserving as a current collector, and drying and pressing the foil. FIG. 6is an illustration of the electrode. In the case of this embodiment, thecoating area (W1×W2) of the electrode 101 was 268×178 mm² and slurry wasapplied to both sides of the current collector 102 of 20 μm thickness ata thickness of 128 μm. As a result, the electrode thickness t was 276μm. One of the edge portions of the shorter side of the currentcollector 102 was not coated in 1 cm width and a tab 103 (aluminum witha thickness of 0.1 mm and a width of 6 mm) was welded.

(2) A negative electrode same as the above negative electrode 1 exceptfor the coating thickness of an electrode was used. Because the shape ofthe negative electrode is the same as the above positive electrode, thenegative electrode is described by referring to FIG. 6. In the case ofthis embodiment, the coating area (W1×W2) of the electrode 101 was270×180 mm² and slurry was applied to both sides of the currentcollector 102 of 14 μm thickness at a thickness of 72 μm. As a result,the electrode thickness t was 158 μm. One of the edge portions of theshorter side of the current collector 102 was not coated in 1 cm widthand a tab 103 (nickel with a thickness of 0.1 mm and a width of 6 mm)was welded.

Only one side was coated in accordance with the same method and asingle-sided electrode of 86 μm thickness was formed by the same methodexcept for the single-sided coating. The single-sided electrode waspositioned at the outermost in the electrode-stacked body in Item (3)(101 c in FIG. 2).

(3) An electrode-stacked body was formed by alternately stacking 10positive electrodes and 11 negative electrodes (including twosingle-sided electrodes) obtained in the above Item (1) with a separator104 (made by TONEN TAPIRUSU Co., Ltd.; made of porous polyethylene) heldbetween each of the layers as shown in FIG. 2.

(4) A bottom case 2 (refer to FIG. 1) of a battery was formed by bendinga thin plate made of SUS304 having a thickness of 0.5 mm and having theshape shown in FIG. 4 inward along the broken lines L1 and moreoverbending it outward along the alternate long and short dash lines L2, andthen arc-welding the corners A. The upper case 1 of the battery was alsoformed of a thin plate made of SUS304 having a thickness of 0.5 mm.Furthermore, positive electrode and negative electrode 3 and 4 made ofSUS304 (diameter of 6 mm) and a safety-vent hole (diameter of 8 mm) wereformed on the upper case 1 and the positive and negative electrodes 3and 4 were insulated from the upper case 1 by a polypropylene packing.

(5) Each positive-electrode tab 103 a of the electrode-stacked bodyformed in the above Item (3) was welded to the positive-electrode tab 3and each negative-electrode tab 103 b of it was welded to thenegative-electrode tab 4 through a connection line and theelectrode-stacked body was set to the bottom case 2 and fixed by aninsulating tape to laser-weld the entire circumference along the edge Ain FIG. 1. Thereafter, a solution made by dissolving LiPF₆ at aconcentration of 1 mol/l in a solvent obtained by mixing ethylenecarbonate and diethyl carbonate at a weight ratio of 1:1 was pouredthrough a safety-vent hole as electrolyte and the hole was closed byusing an aluminum foil having a thickness of 0.1 mm.

(6) The formed battery has a size of 300 mm×210 mm×6 mm. The battery wascharged by a constant-current/constant-voltage charging for 18 hours, inwhich the battery was charged up to 4.3 V by a current of 3 A and thencharged by a constant voltage of 4.3 V. Then, the battery was dischargedto 2.0 V by a constant current of 3 A. The discharge capacity was 27.6Ah, the energy capacity was 99 Wh, and the volume energy density was 263Wh/l.

(7) As a result of charging the battery and discharging the battery at acurrent of 30A in a thermostatic chamber at 20 degree Celsius by themethod described in the above Item (6), rise of the battery temperatureat the end of discharge was small compared with the case of assembledprismatic battery (thickness of 12 mm or more) having the same capacity.

Embodiment 3-2

A positive electrode was formed which was the same as that of theembodiment 3-1 except that slurry was applied to both sides of a currentcollector 102 at a thickness of 130 μm and the electrode thickness t was280 μm.

Then, a negative electrode was used which was the same as the abovenegative 4 except for the coating thickness of the electrode. Thecoating area (W1×W2) of an electrode 101 is 270×180 mm² and slurry isapplied to both sides of the current collector 102 of 14 μm at athickness of 70 μm. As a result, the electrode thickness t is 154 μm. Tslurry was applied to only one side by the same method and asingle-sided electrode having a thickness of 84 μm was formed inaccordance with the same method except for the single-sided applicationof the slurry. Other points were the same as those of the embodiment3-1.

As a result of forming a battery by the same method as the case of theembodiment 3-1 and measuring the capacity, the capacity was 28.2 Ah. Tthe energy capacity was 102 Wh and the volume energy density was 269Wh/l.

Furthermore, a battery was formed under the same condition as the caseof each of the above embodiment by using the above negative electrodes2, 3, and 5 to 7 except for the negative electrodes 1 and 4 and theresult same as the above was obtained.

COMPARATIVE EXAMPLE 3-1 For Comparison With Embodiments 3-1 and 3-2

A positive electrode was formed which was the same as that of theembodiment 3-1 except that slurry was applied to both sides of a currentcollector 102 and the electrode thickness t was 260 μm.

Then, a negative electrode was used which was same as the above negativeelectrode 8 except for the coating thickness of the electrode. In thecase of this comparative example, the coating area (W1×W2) of anelectrode 101 was 270×180 mm² and slurry was applied to both sides ofthe current collector 102 of 14 μm thickness at a thickness of 80 μm. Asa result, the electrode thickness t was 174 μm. A slurry was applied toonly one side by the same method and a single-sided electrode of 94 μmwas formed in w accordance with the same method except for thesingle-sided application of the slurry. Other points were the same asthe case of the embodiment 3-1.

As a result of forming a battery in accordance with the same method asthe case of the embodiment 3-1 and measuring the capacity, the capacitywas 25.8 Ah. The energy capacity was 93 Wh and the volume energy densitywas 249 Wh/l which were lower than the case of the embodiment 3-1 .

[C-Type Negative Electrode]

(Formation of Electrode)

Fifty grams of artificial graphite (“KS-44” made by RONZA Co., Ltd.,central particle diameter D50=20.1 mm, particle size distribution of 0.1to 150 mm, d002=0.336 nm, Lc=110 nm, La=105 nm, specific surfacearea=8.2 m²/g, R value=0.23, true specific gravity of 2.25 g/cm³) and 5g of coal tar pitch from which primary QI was previously removed andwhich had a softening point of 80 degree Celsius (quinoline-insolublecomponent=trace, toluene-insoluble component=30%), and 50 g of tarmiddle oil were poured in a 500 ml separable flask and distilled at 200degree Celsius and 10 Torr. After recovering tar middle oil,distillation was stopped to obtain pitch-coating graphite.

Because the measured value of the quinoline-soluble component of theobtained pitch coating graphite was 6.8%, the coating ratio ofcoat-forming carbon (volatile-component contained carbon) was equal to0.068. A coating layer was carbonized by mixing 100 parts by weight ofartificial graphite (“KS-44” made by RONZA Co., Ltd.; the property wasthe same as the above mentioned) with 100 parts by weight of the pitchcoating graphite and heat-treating the mixture in a nitrogen atmosphereat 1,200 degree Celsius for 1 hour (temperature rise rate of 50 degreeCelsius/hour). The specific surface area of the obtained coatinggraphite particles was 2.5 m²/g and the average particle diameter was20.3 mm. An electrode was formed by using the coating-graphite particlesas a negative-electrode active material, acetylene black (“DENKA BLACK”made by DENKI KAGAKU KOGYO K.K.) as a conductive material, and asolution obtained by dissolving polyvinylidene fluoride (“KF#1101” madeby Kureha Chemical Industry Co., Ltd.) in N-methylpyrrolidone as abinder.

In this case, the blending ratio was set to the following ratio;coating-graphite particles: acetylene black: polyvinylidenefluoride=87:3:10 (weight ratio).

Three types of negative electrodes 1′ to 3′ respectively having athickness of 100 μm were formed by applying the above solution to copperfoil of 14 μm thickness with various thickness and then, drying it at 80degree Celsius for 15 min, and continuously pressing it with a rollerpress having a radius of curvature of 30 cm.

A capacity test was performed in accordance with the above method byusing the above negative electrodes. As an electrolyte, a solution wasused which was obtained by dissolving LiPF₆ having a concentration of 1mol/kg in a mixed solvent consisting of a ratio of ethylene carbonate :dimethyl carbonate : methyl ethyl carbonate=7:6:6 (weight ratio). Table3 shows obtained electrode densities, initial capacities, and initialefficiencies.

A negative electrode 4′ was formed similarly to the case of the negativeelectrode 1′ except for using graphitized MCMB (made by OSAKA GASCHEMICAL; product No. 6-28). Table 3 shows obtained electrode densities,initial capacities, and initial efficiencies. TABLE 3 Negative electrodeElectrode density Initial capacity Initial No. (g/cm³) (mAh/cm³)efficiency (%) Negative electrode 1.35 411 91 1′ Negative electrode 1.46441 91 2′ Negative electrode 1.54 471 90 3′ Negative electrode 1.44 36589 4′

As shown in Table 3, the negative electrodes 1′ to 3′ have electrodedensities of 1.35 to 1.60 g/cm³, and each of them has a capacity of 400mAh/cm³ or more, and has large capacity compared with the capacity ofthe negative electrode 4′ using graphitized MCMB.

Embodiment 4- 1

(1) A positive-electrode mixture slurry was obtained by mixing 100 partsby weight of spinel-type LiMn₂O₄ (made by SEIMI CHEMICAL; product No.M063), 10 parts by weight of acetylene black, and 5 parts by weight ofpolyvinylidene fluoride (PVdF) with 100 parts by weight ofN-methylpyrrolidone (NMP). A positive electrode was obtained by applyingthe slurry to both sides of an aluminum foil having a thickness of 20 μmserving as a current collector, and drying and pressing the foil. FIG. 6is an illustration of an electrode. In the case of this embodiment, thecoating area (W1×W2) of the electrode 101 was 268×178 mm² and slurry wasapplied to both sides of the current collector 102 of 20 μm thickness ata thickness of 128 μm. As a result, the electrode thickness t was 276μm. One of the edge portions of the shorter side of the currentcollector 102 was not coated in 1 cm width and a tab 103 (aluminum witha thickness of 0.1 mm and a width of 6 mm) was welded.

(2) A negative electrode was used which was the same as the abovenegative electrode 2′ except for the coating thickness of an electrode.Because the shape of the negative electrode is the same as the abovepositive electrode, the negative electrode was described by referring toFIG. 6. In the case of this embodiment, the coating area (W1×W2) of theelectrode 101 was 270×180 mm² and slurry was applied to both sides ofthe current collector 102 of 14 μm thickness at a thickness of 72 μm. Asa result, the electrode thickness t was 158 μm. One of the edge portionsof the shorter side of the current collector 102 was not coated in 1 cmwidth and a tab 103 (nickel with a thickness of 0.1 mm and a width of 6mm) was welded.

Slurry was applied to only one side by the same method and asingle-sided electrode having a thickness of 86 μm was formed by thesame method except for the single-side application of the slurry. Thesingle-sided electrode was set to the outermost of the stackedelectrodes in Item (3) (101 c in FIG. 2).

(3) An electrode-stacked body was formed by alternately stacking 10positive electrodes and 11 negative electrodes (including twosingle-sided electrodes) obtained in the above Item (1) with a separator104 (made by TONEN TAPIRUSU Co., Ltd.; made of porous ethylene) heldbetween each of the electrode as shown in FIG. 2.

(4) A bottom case 2 (refer to FIG. 1) of a battery was formed by bendinga thin plate made of SUS304 having a thickness of 0.5 mm and having theshape shown in FIG. 4, inward along the broken lines L1 and moreoverbending it outward along the alternate long and short dash lines L2, andthen arc-welding the corners A. The upper case 1 of the battery was alsoformed of a thin plate made of SUS304 having a thickness of 0.5 mm.Furthermore, positive electrode and negative electrode 3 and 4 (diameterof 6 mm) and a safety-vent hole (diameter of 8 mm) were formed on theupper case 1 but the positive and negative electrodes 3 and 4 wereinsulated from the upper case 1 by a polypropylene packing.

(5) Each positive-electrode tab 103 a of the electrode-stacked bodyformed in the above Item (3) was welded to the positive-electrode tab 3and each negative-electrode tab 103 b of it was welded to thenegative-electrode tab 4 through a connection line and theelectrode-stacked body was set to the bottom case 2 and fixed by aninsulating tape to laser-weld the entire circumference along the edge Ain FIG. 1. Thereafter, a solution was made by dissolving LiPF₆ at aconcentration of 1 mol/l in a solvent obtained by mixing ethylenecarbonate and diethyl carbonate at a weight ratio of 1:1, and thesolution was poured through a safety-vent hole as electrolyte. The holewas closed by using aluminum foil having a thickness of 0.1 mm.

(6) The formed battery had a size of 300 mm×210 mm×6 mm. The battery wascharged by a constant-current/constant-voltage charging for 18 hours, inwhich the battery was charged up to 4.3 V by a current of 3 A and thencharged by a constant voltage of 4.3 V. Then, the battery was dischargedto 2.0 V by a constant current of 3 A. The discharge capacity was 27.6Ah, energy capacity was 99 Wh, and volume energy density was 263 Wh/l.

(7) As a result of charging the battery and discharging the battery at acurrent of 30 A in a thermostatic chamber at 20 degree Celsius by themethod described in the above Item (6), rise of the battery temperatureat the end of discharge was small compared with the case of theassembled prismatic battery (thickness of 12 mm or more) having the samecapacity.

A battery was formed under the same conditions as the case of theembodiment 4-1 by using negative electrodes same as the above negativeelectrodes 1′ and 3′ except for the coating thickness of an electrode,and the same result as the above was obtained.

COMPARATIVE EXAMPLE 4-1 For Comparison With Embodiment 4-1

A positive electrode was formed which was the same as that of theembodiment 4-1 except that slurry was applied to both sides of a currentcollector 102 and the electrode thickness t was 260 μm.

Then, a negative electrode same as the above negative electrode 4′except for the coating thickness of the electrode was used. In the caseof this comparative example, the coating area (W1×W2) of an electrode101 was 270×180 mm² and slurry was applied to both sides of the currentcollector 102 of 14 μm thickness at a thickness of 80 μm. As a result,the electrode thickness t was 174 μm. A slurry was applied to only oneside by the same method and a single-sided electrode of 94 μm was formedin accordance with the same method except for the single-sideapplication of the slurry. Other points were the same as the case of theembodiment 4- 1.

As a result of forming a battery in accordance with the same method asthe case of the embodiment 4-1 and measuring the capacity, the capacitywas 25.6 Ah. The energy capacity was 91 Wh and the volume energy densitywas 240 Wh/l which were lower than the case of the embodiment 4-1.

Now, descriptions of embodiments of A, B, and C-type negative electrodesare completed.

[Preferable Separator Used for Non-Aqueous Secondary Battery of thePresent Invention]

In the case of the present invention, it was also allowed that thepositive electrode 101 a and negative electrode 101 b (or negativeelectrode 101 c positioned at both outer sides in the stackedelectrodes) were alternately stacked with the separator 104 held betweeneach of the layers as shown in FIG. 2.

It is preferable to use A- or B-type separator described below in detailalthough the use is not limited thereby.

Forming a non-aqueous secondary battery using the above separator into aflat shape is advantageous for heat radiation because the radiation areaincreases. The thickness of the secondary battery is preferably lessthan 12 mm, more preferably less than 10 mm, or still more preferablyless than 8 mm. The lower limit of the thickness of 2 mm or more ispractical when considering a packing rate of an electrode and a batterysize (to obtain the same capacity, the area increases as the thicknessdecreases). When the thickness of the battery becomes 12 mm or more, itis difficult to sufficiently radiate the heat in the battery to theoutside or the temperature difference between the inner portion of thebattery and the vicinity of the surface of the battery increases andfluctuations of charge quantity and voltage in the battery increasebecause the internal resistance differs. Though a specific thickness isproperly determined in accordance with a battery capacity or energydensity, it is preferable to design a battery at a maximum thickness atwhich an expected heat radiation characteristic is obtained.

[A-Type Separator]

An A-type separator 104 is described below in detail. FIG. 7 is anillustration showing results of measuring the thickness of the separator104 while pressing the separator 104 in the thickness direction of theseparator 104. In FIG. 7, X denotes a tangent of the thickness-pressurecurve of the separator at the pressure F, and Y denotes athickness-pressure curve of the separator.

First, the condition required for the separator 104 is as follows: whenpressing the separator 104 at a pressure of 2.500 kg/cm², the thicknessA of the separator 104 is in a range not less than 0.02 mm and not morethan 0. 15 mm or preferably in a range not less than 0.02 mm and notmore than 0.10 mm. Such a case in which the thickness A under pressureexceeds 0.15 mm is not preferable because the thickness of the separator104 is too large, the internal resistance increases or the ratio of theseparator 104 occupying the inside of the battery increases, and asufficient capacity cannot be obtained. However, such a case in whichthe thickness A under pressure is less than 0.02 mm is not practicallypreferable because it is difficult to manufacture the separator.

As shown in FIG. 7, the separator 104 is resilient. Therefore, whenapplying a load to the separator 104 in its thickness direction (in FIG.7, the abscissa shows pressure applied to the separator), the thicknessof the separator 104 quickly decreases at the initial time. However,when further increasing the load, the change of the thickness of theseparator 104 slowly decreases and then, the thickness hardly changeseven if further applying the load. In this case, it is an importantpoint that a separator assembled into a battery has resiliency. It isalso important that the pressure applied to the separator is low in thecase of a non-aqueous secondary battery although the pressure changesdepending on the battery size, wall thickness or wall material of thecase, or other design factors, and that the separator has resiliency atsuch a low pressure. Therefore, in preferable separator, when theabsolute value of the change rate of the thickness of the separator 104to a pressure (kg/cm²) (in FIG. 7, the absolute value of the tilt of thetangent line of the thickness-pressure curve Y of a separator at thepressure F, e.g. the absolute value of the tilt of the tangent line X)is defined as B (mm/(kg/cm²)), the pressure F which renders B/A=1 is ina range not less than 0.050 kg/cm² and not more than 1.000 kg/cm² ormore preferably in a range not less than 0.050 kg/cm² and not more than0.700 kg/cm². A case in which the pressure F is lower than 0.050 kg/cm²is not preferable because a separator already loses resiliency and asufficient cycle characteristic is not obtained. A case in which thepressure F exceeds 1.000 kg/cm² is not preferable because a separatorfrequently has a very high resiliency and therefore, it is difficult tobuild the separator in a battery.

The porosity of the separator 104 is 40% or more, preferably 50% or moreunder the pressure of 2.500 kg/cm², that is, when the separator has theabove thickness A mm. A case in which the porosity is less than 40% isnot preferable because an electrolyte cannot be sufficiently held, theinternal resistance increases, or a sufficient cycle characteristic isnot obtained.

It is preferable to use non-woven fabric as a separator meeting theabove conditions. In this case, the separator can be easilymanufactured. Because non-woven fabric for a battery is finally finishedby using a technique such as thermal pressing in order to adjust thethickness. Non-woven fabric- has been frequently lost resiliency in theabove thickness-adjusting step (some of non-woven fabrics used forclothing do not include the thickness-adjusting step and most non-wovenfabrics are resilient). However, a separator used for a non-aqueoussecondary battery of the present invention can be easily manufactured byproperly setting a condition such as the thermal pressing.

Though a material of the separator 104 is not limited, it is possible touse polyolefin such as polyethylene or polypropylene, polyamide, kraftpaper, glass, etc. However, polyethylene or polypropylene is preferablefrom the viewpoints of cost and moisture. Furthermore, when usingpolyethylene or polypropylene for the separator 104, the unit weight ofthe separator is preferably not less than 5 g/m² and not more than 30g/m², more preferably not less than 5 g/m² and not more than 20 g/m², orstill more preferably not less than 8 g/m² and not more than 20 g/m². Acase in which the unit weight of a separator exceeds 30 g/m² is notpreferable because the separator becomes too thick or the porositylowers and the internal resistance of a battery increases. A case inwhich the unit weight is less than 5 g/m² is not preferable because apractical strength cannot be obtained.

The A-type separator is more minutely described below by using anembodiment of the separator.

Embodiment 5-1

(1) A positive-electrode mixture slurry was obtained by mixing 100 partsby weight of LiCoO₂, 8 parts by weight of acetylene black, and 3 partsby weight of polyvinylidene fluoride (PVdF) with 100 parts by weight ofN-methylpyrrolidone (NMP). A positive electrode was obtained by applyingthe slurry to both sides of aluminum foil having a thickness of 20 μmserving as a current collector, and drying and pressing the foil. FIG. 6is an illustration of an electrode. In the case of this embodiment, thecoating area (W1×W2) of the electrode 101 is 268×178 mm² and slurry wasapplied to both sides of the current collector 102 of 20 μm thickness ata thickness of 105 μm. As a result, the electrode thickness t is 230 μm.One of the edge portions of the shorter side of the current collector102 was not coated in 1 cm width and a tab 103 (aluminum with athickness of 0.1 mm and a width of 6 mm) was welded.

(2) A negative-electrode mixture slurry was obtained by mixing 100 partsby weight of graphitized mesocarbon microbeads (MCMB, made by OSAKA GASCHEMICAL Co., Ltd., product No. 6-28) and 10 parts by weight of PVdFwith 90 parts by weight of NMP. A negative electrode was obtained byapplying the slurry to both sides of copper foil having a thickness of14 μm serving as a current collector, drying the foil and then pressingthe foil. Because the shape of the electrode is the same as that of theabove-described positive electrode, the negative electrode is describedbelow by referring to FIG. 6. In the case of this embodiment, thecoating area (W1×W2) of the electrode 101 was 270×180 mm² and the slurrywas applied to both sides of the current collector 102 of 14 μmthickness at a thickness of 110 μm. As a result, the electrode thicknesst was 234 μm. One of the edge portions of the shorter side of thecurrent collector 102 was not coated in 1 cm width and a tab 103 (nickelwith a thickness of 0.1 mm and a width of 6 mm) was welded.

Slurry was applied to only one side in accordance with the same methodand a single-sided electrode having a thickness of 124 μm was inaccordance with the same method formed except for the single-sideapplication of the slurry. The single-sided electrode was set to theoutermost of the stacked electrodes in Item (3) (101 c in FIG. 2).

(3) An electrode-stacked body was formed by alternately stacking 8positive electrodes and 9 negative electrodes (including twosingle-sided electrodes) obtained in the above Item (1) with a separator104 (polyethylene-polypropylene non-woven fabric) held between each ofthe electrodes. Table 4 shows characteristics of the separator.

A pressure F was calculated by stacking five separators respectively cutinto 5×5 cm² and measuring a pressure-thickness curve initially every0.005 kg/cm² and then every 0.025 kg/cm² in a range from 0.025 kg/cm² upto 0.500 kg/cm² and then every 0.100 kg/cm² in a range from 0.500 kg/cm²up to 2.50 kg/cm² in accordance with the method described by referringto FIG. 7. Though measurement was repeated three times every 5 hours,the value of F and the thickness A under pressure of 2.500 kg/cm² werehardly changed.

(4) The bottom case 2 of the battery (refer to FIG. 1) was formed bywringing a 0.5 mm thin plate made of SUS304 into a depth of 5 mm. Theupper case 1 of the battery was also formed of a 0.5 mm thin plate madeof SUS304. The positive and negative electrodes made of SUS304 3 and 4(diameter of 6 mm) were set to the upper case and a safety-vent hole(diameter of 8 mm) was formed on the upper case and the positive andnegative electrodes 3 and 4 were insulated from the upper case 1 by apolypropylene packing.

(5) Each positive-electrode tab 103 a of the electrode-stacked bodyformed in the above Item (3) was welded to the positive-electrode tab 3and each negative-electrode tab 103 b of it was welded to thenegative-electrode tab 4 through a connection line and theelectrode-stacked body was set to the bottom case 2 and fixed by aninsulating tape to laser-weld the entire circumference of the corner Ain FIG. 1. Thereafter, a solution made by dissolving LiPF₆ at aconcentration of 1 mol/l in a solvent obtained by mixing ethylenecarbonate and diethyl carbonate at a weight ratio of 1:1 was pouredthrough a safety-vent hole as an electrolyte and the hole was closed byusing aluminum foil having a thickness of 0.1 mm.

(6) The obtained battery was charged by aconstant-current/constant-voltage charging for 8 hours, in which thebattery was charged up to 4.1 V by a current of 5 A and then charged bya constant voltage of 4.1 V. Then, the battery was discharged up to 2.5V by a constant current of 10 A. The discharge capacity was 23.3 Ah. Thetemperature rise of the battery while discharged was small compared withthe case of a prismatic battery (battery having a thickness of 12 mm ormore) having the same capacity.

(7) The capacity when repeating charge and discharge by 10 cycles byusing the battery under the same condition as the above mentioned was21.5 Ah.

Embodiment 5-2

A battery was formed similarly to the case of the embodiment 5-1 exceptfor using the polypropylene non-woven fabric of the embodiment 5-2 shownin Table 4 as a separator. The battery was charged by aconstant-current/constant-voltage charging for 8 hours, in which thebattery was charged up to 4.1 V by a current of 5 A and then charged bya constant voltage of 4.1 V. Then, the battery was discharged up to 2.5V by a constant current of 10 A. The discharge capacity was 22.8 Ah. Thecapacity when repeating charge and discharge by 10 cycles under the samecondition as the case of the embodiment 5-1 by using the battery was20.9 Ah.

COMPARATIVE EXAMPLE 5-1 For Comparison With Embodiments 5-1 and 5-2

A battery was formed similarly to the case of the embodiment 5-1 exceptfor using the polyethylene micro-porous film of the comparative example5-1 shown in Table 4 as a separator and change the number of layeredelectrodes to 10 positive electrodes and 11 negative electrodes(including two single-sided electrodes). The battery was charged by aconstant-current/constant-voltage charging for 8 hours, in which thebattery was charged up to 4.1 V by a current of 5 A and then charged bya constant voltage of 4.1 V. Then, the battery was discharged up to 2.5V by a current of 10 A. The discharge capacity was 25.2 Ah. The capacitywhen repeating charge and discharge by 10 cycles under the samecondition as the case of the embodiment 5-1 by using the battery was19.0 Ah.

The separator is used for, for example, an 18650-type cylindricalbattery. In the case of the cylindrical battery, cycle deterioration at10 initial cycles is 90% or more. However, when using a flat battery,the discharge capacity was lowered up to the 10th cycle though theinitial capacity was high because a separator was thin and the number oflayered electrodes was large compared with Embodiments 5-1 and 5-2.

COMPARATIVE EXAMPLE 5-2

A battery was formed similarly to the case of the embodiment 5-1 exceptfor using the polypropylene non-woven fabric (pressure F exceeds 0.025kg/cm² but it is lower than 0.050 kg/cm²) of the comparative example 5-2shown in Table 4 as a separator. The battery was charged by aconstant-current/constant-voltage charging for 8 hours, in which thebattery was charged up to 4.1 V by a current of 5 A and then charged bya constant voltage of 4.1 V. Then, the battery was discharged up to 2.5V by a constant current of 10 A. The discharge capacity was 21.0 Ah. Thecapacity when repeating charge and discharge by 10 cycles under the samecondition as the case of the embodiment 5-1 by using the battery was17.0 Ah.

Though the separator was the same as the separator of the embodiment 5-1in porosity and thickness, it was not resilient. Therefore, when usingthe separator for a flat battery, the discharge capacity was lowered upto the 10th cycle.

COMPARATIVE EXAMPLE 5-3

A battery was formed similarly to the case of the embodiment 5-1 exceptfor using the glass non-woven fabric of the comparative example 5-3shown in Table 4 as a separator and change the number of layeredelectrodes to 6 positive electrodes and 7 negative electrodes (includingtwo single-sided electrodes). The battery was charged by aconstant-current/constant-voltage charging for 8 hours, in which thebattery was charged up to 4.1 V by a current of 4 A and then charged bya constant voltage of 4.1 V. Then, the battery was discharged up to 2.5V by a current of 8 A. The discharge capacity was 18.1 Ah. The capacitywhen repeating charge and discharge by 10 cycles under the samecondition as the case of the embodiment 5-1 by using the battery was17.3 Ah.

The separator is sufficiently resilient and has a capacity retentionrate equal to those of the embodiments 5-1 and 5-2 after 10 cycles pass.However, because the separator has a large thickness, the capacity waslower than those of the embodiments 5-1 and 5-2. TABLE 4 PorosityThickness Pressure at 2.5 Unit A F kg/cm² weight Material (mm) (kg/cm²)(%) (g/m²) Embodiment Polyethylene 0.087 0.500 89.1 13.7 5-1polypropylene non-woven fabric Embodiment Polypropylene 0.072 0.050-83.0 13.1 5-2 non-woven 0.075 fabric Comparative Polyethylene 0.025<0.025 41.0 15.5 example 5-1 micro-porous film Comparative Polypropylene0.100 0.025< 73.0 32 example 5-2 non-woven <0.050 fabric ComparativeGlass non- 0.232 0.200 >90 — example 5-3 woven fabric

[B-Type Separator]

A B-type separator is described below in detail. FIG. 8 shows a sideview and a perspective view of a separator used for the non-aqueoussecondary battery shown in FIG. 1. As shown in FIG. 8, the separatorcomprises a first separator 104 a and two second separators 104 b, inwhich the second separators 104 b were arranged at both sides of thefirst separator 104 a. The configuration of the separator is notlimited. Two or more different types of separators can be used as longas the separators meet the following conditions. For example, one firstseparator 104 a and one second separator 104 b arranged as shown in FIG.9 may be used, or separators of different types may be used instead ofsecond separators 104 b of the same type shown in FIG. 8, or a secondseparator may be placed between two first separators in contrary to whatis shown in FIG. 8.

Then, a first separator is more minutely described below. FIG. 7 is anillustration showing results of measuring the thickness of the firstseparator while applying a pressure to the first separator in itsthickness direction. In FIG. 7, X denotes a tangent of the thicknesscurve of the separator to pressure at a pressure F and Y denotes athickness curve of the separator to pressure.

First, when pressing the first separator at a pressure of 2.500 kg/cm²as a condition required for the first separator, the thickness A of thefirst separator is kept in a range not less than 0.02 mm and not morethan 0.15 mm, or preferably kept in a range not less than 0.02 mm andnot more than 0.10 mm. A case in which the thickness under pressureexceeds 0.15 mm is not preferable because the thickness of the separatoris too large, the internal resistance increases or the rate for theseparator to occupy the inside of a battery increases, and a sufficientcapacity is not obtained. However, a case in which the thickness A underpressure is less than 0.02 mm is not preferable for practical usebecause it is difficult to manufacture the battery.

As shown in FIG. 7, the first separator is resilient and when applying aload to the first separator in its thickness direction (in FIG. 7,abscissa shows pressure applied to separator), the thickness of thefirst separator quickly decreases at the initial point of time. However,when further increasing a load, change of the thickness of the firstseparator slowly decreases and then, thickness is hardly changed. Inthis case, it is important that a separator is resilient when a batteryis formed. In the case of a flat non-aqueous secondary battery, thebattery size, or wall thickness or wall material of a case are changeddepending on other design elements. However, it is important that apressure to be applied to a separator is low and the separator isresilient at a low pressure. Therefore, in a preferable separator, whenassuming the absolute value of the change rate of the thickness (mm) ofthe first separator to a pressure (kg/cm²) (in FIG. 7, tangent ofthickness curve Y of separator to pressure at pressure F, such asabsolute value of tilt of tangent X) as B (mm/(kg/cm²)), the pressure Fin which B/A is equal to 1 is not less than 0.050 kg/cm² and not morethan 1.000 g/cm² or more preferably not less than 0.050 kg/cm² and notmore than 0.700 kg/cm². A case in which the pressure F is lower than0.050 kg/cm² is not preferable because a separator already loses itsresiliency when a battery is formed and a sufficient cyclecharacteristic is not obtained or a case in which the pressure F exceeds1.000 kg/cm² is not preferable because a separator frequently has a verylarge resiliency and it is difficult to set the separator in a battery.

When the porosity of the first separator at a pressure of 2.500 kg/cm²,that is, at the above thickness of A mm is kept at 40% or more orpreferably kept at 50% or more. A case in which the porosity is lessthan 40% is not preferable because an electrolyte cannot be sufficientlykept, the internal pressure rises, or a sufficient cycle characteristiccannot be obtained.

It is preferable to use non-woven fabric for the first separator meetingthe above conditions. In this case, it is easy to manufacture theseparator. In general, non-woven fabric for a battery is finallyfinished in order to adjust the thickness by a technique such as thermalpressing. Non-woven fabric has frequently lost its resiliency so far inthe thickness-adjusting step (some of non-woven fabrics for clothing donot have the thickness-adjusting step and most non-woven fabrics areresilient). However, a separator used for a non-aqueous secondarybattery of the present invention can be easily manufactured by properlysetting a condition such as the above thermal pressing.

Then, the second separator is more minutely described below. The secondseparator is a micro-porous film having a pore diameter of 5 μm or lessor preferably having a pore diameter of 2 μm or less and having aporosity of 25% or more or preferably having a porosity of 30% or more.A pore diameter can be observed by an electron microscope. The abovemicro-porous film can use a micro-porous film generally marketed for alithium ion battery. The second separator is used to compensate adisadvantage that a slight short circuit easily occurs when the batteryis manufactured or charged or discharged because the separator has acomparatively large pore diameter and a high porosity. Therefore, a casein which the pore diameter of the second separator exceeds 5 μm is notpreferable because it is impossible to compensate the abovedisadvantage. A case in which the porosity is less than 25% is notpreferable because an electrolyte cannot be sufficiently kept or theinternal resistance rises. Furthermore, because the thickness of thesecond separator is 0.05 mm or less, it is possible to use a separatorhaving a thickness of not more than 5 μm and not more than 30 μm. Thisis because it is difficult to manufacture the separator if the thicknessis too small or the internal resistance tends to rise if the thicknessis too large.

Materials of the first and second separators are not limited. Forexample, it is possible to use polyolefins such as polyethylene andpolypropylene, and polyamide, kraft paper, and glass. However,polyethylene and polypropylene are preferable from the viewpoints ofcost and moisture.

When using polyethylene or polypropylene for the first separator, theunit weight of the first separator is preferably not less than 5 g/m²and 30 g/m², more preferably not less than 5 g/m² and not more than 20g/m², or still more preferably not less than 8 g/m² and not more than 20g/m^(2.) A case in which the unit weight of a separator exceeds 30 g/m²is not preferable because the separator becomes too thick, the porositylowers, or the internal resistance of a battery rises. A case in whichthe unit weight is less than 5 g/m² is not preferable because a strengthfor practical use cannot be obtained.

Though various combinations of materials of the first and secondseparators can be considered, it is preferable to combine differentmaterials. In this case, the effect of shutdown of the operation of thebattery is further expected, in which the shutdown occurs when a batterycauses thermal runaway.

It is preferable to manufacture the first and second separators bylaminating them together. To laminate them together, the followingmethod can be used: mechanical mutual laminating by pressing, mutuallaminating by thermal rollers, mutual laminating by chemicals, or mutuallaminating by adhesive. For example, to combine one separator mainlymade of polyethylene with the other separator mainly made ofpolypropylene, it is allowed to laminate them while melting the surfacelayer of the polyethylene separator by a thermal roller, takingpolyethylene powder into polypropylene non-woven fabric, or laminatingnon-woven fabrics made of a material obtained by coating the surface ofpolypropylene fiber with polyethylene together by thermal rollers. It isimportant to perform mutual laminating without crushing voids of theabove separators.

Embodiments of a B-type separator are more specifically described below.

Embodiment 6-1

(1) A positive-electrode mixture slurry was obtained by mixing 100 partsby weight of LiCo₂O₄, 8 parts by weight of acetylene black, and 3 partsby weight of polyvinylidene fluoride (PVdF) with 100 parts by weight ofN-methylpyrrolidone (NMP). A positive electrode was obtained by applyingthe slurry to both sides of aluminum foil having a thickness of 20 μmserving as a current collector, and drying and pressing the foil. FIG. 6is an illustration of an electrode. In the case of this embodiment, thecoating area (W1×W2) of the electrode 101 is 268×178 mm² and slurry wasapplied to both sides of the current collector 102 of 20 μm thickness ata thickness of 95 μm. As a result, the electrode thickness t was 210 μm.One of the edge portions of the shorter side of the current collector102 was not coated in 1 cm width and a tab 103 (aluminum with athickness of 0.1 mm and a width of 6 mm) was welded.

(2) A negative-electrode mixture slurry was obtained by mixing 100 partsby weight of graphitized mesocarbon microbeads (MCMB, made by OSAKA GASCHEMICAL Co., Ltd., product No. 6-28) and 10 parts by weight of PVdFwith 90 parts by weight of NMP. A negative electrode was obtained byapplying the slurry to both sides of copper foil having a thickness of14 μm serving as a current collector, drying the foil and then pressingthe foil. Because the shape of the electrode is the same as that of theabove-described positive electrode, the negative electrode is describedbelow by referring to FIG. 6. In the case of this embodiment, thecoating area (W1×W2) of the electrode 101 was 270×180 mm² and the slurrywas applied to both sides of the current collector 102 of 14 μmthickness at a thickness of 105 μm. As a result, the electrode thicknesst was 224 μm. One of the edge portions of the shorter side of thecurrent collector 102 was not coated in 1 cm width and a tab 103 (nickelwith a thickness of 0.1 mm and a width of 6 mm) was welded.

Slurry was applied to only one side in accordance with the same methodand a single-sided electrode having a thickness of 119 μm was formed inaccordance with the same method except for the single-sided applicationof the slurry. The single-sided electrode is set to the outermost of theelectrode-stacked body in Item (3) (101 c in FIG. 2).

(3) In the case of this embodiment, as shown in Table 5, anelectrode-stacked body was formed by using polyethylene-polypropylenenon-woven fabric as a first separator and a polyethylene micro-porousfilm as a second separator so that the positive-electrode side became amicro-porous film, stacking the first and second separators similarly tothe case of the separators shown in FIG. 9, and alternately stacking 8positive electrodes and 9 negative electrodes (including twosingle-sided electrodes) obtained in the above Item (1) through aseparator 104 (constituted by stacking a polyethylene-polypropylenenon-woven fabric and a polypropylene micro-porous film). Table 5 showscharacteristics of the separators.

A pressure F was calculated in accordance with the method described forFIG. 7 by stacking five separators respectively cut into 5×5 cm² andmeasuring the pressure-thickness curve of the first separator at firstevery 0.005 kg/cm², and then every 0.025 kg/cm² in the pressure rangefrom 0.025 kg/cm² up to 0.500 kg/cm² and every 0.100 kg/cm² in thepressure range from 0.500 kg/cm² up to 2.500 kg/cm². As a result ofrepeating the above measurement three times every 5 hours, the value ofF and the thickness A at a pressure of 2.500 kg/cm² were hardly changed.

(4) The bottom case 2 of the battery (refer to FIG. 1) was formed bydeep drawing of a 0.5 mm thin plate made of SUS304 into a depth of 5 mm.The upper case 1 of the battery was also formed of a 0.5 mm thin platemade of SUS304. The positive and negative electrodes made of SUS304 3and 4 (diameter of 6 mm) were set to the upper case and a safety-venthole (diameter of 8 mm) was formed on the upper case but the positiveand negative electrodes 3 and 4 were insulated from the upper case 1 bya polypropylene packing.

(5) Each positive-electrode tab 103 a of the electrode-stacked bodyformed in the above Item (3) was welded to the positive-electrode tab 3and each negative-electrode tab 103 b of it was welded to thenegative-electrode tab 4 through a connection line and theelectrode-stacked body was set to the bottom case 2 and fixed by aninsulating tape to laser-weld the entire circumference of the corner Ain FIG. 1. Thereafter, a solution made by dissolving LiPF₆ at aconcentration of 1 mol/l in a solvent obtained by mixing ethylenecarbonate and diethyl carbonate at a weight ratio of 1:1 was pouredthrough a safety-vent hole as an electrolyte and the upper case wasclosed by using aluminum foil having a thickness of 0.1 mm. The total offive batteries were formed as described above.

(6) The obtained battery was charged by aconstant-current/constant-voltage charging for 8 hours, in which thebattery was charged up to 4.1 V by a current of 5 A and then charged bya constant voltage of 4.1 V. Then, the batteries were discharged up to2.5 V by a constant current of 10 A. Discharge capacities of the fivebatteries ranged between 21.1 and 21.4 Ah. The temperature rise of thebatteries while discharged was small compared with the case of aprismatic battery (battery having a thickness of 12 mm or more) havingthe same capacity.

(7) Capacities when repeating charge and discharge by 10 cycles underthe same condition as the above by using the above five batteries rangedbetween 19.2 and 20.1 Ah.

Embodiment 6-2

A battery was formed similarly to the case of the embodiment 6-1 exceptfor using the polypropylene non-woven fabric of the embodiment 6-2 shownin Table 5 as a first separator. The battery was charged by aconstant-current/constant-voltage charging for 8 hours, in which thebattery was charged up to 4.1 V by a current of 5 A and then charged bya constant voltage of 4.1 V. Then, the battery was discharged up to 2.5V by a constant current of 10 A. The discharge capacity was 21.0 Ah. Thecapacity when repeating charge and discharge by 10 cycles under the samecondition as the case of the embodiment 6-1 by using the battery was19.0 Ah.

COMPARATIVE EXAMPLE 6-1 For Comparison With Embodiment 6-1

Five batteries were formed similarly to the case of the embodiment 6-1except for using only the polyethylene-polypropylene non-woven fabricsame as the first separator of the embodiment 6-1 shown in Table 5 as afirst separator without using a second separator and change the numberof stacked electrodes to 8 positive electrodes (thickness of either-sideelectrode layer was 105 μm) and 9 negative electrodes (including twosingle-sided electrodes and thickness of either-side electrode layer was110 μm). The battery was charged by a constant-current/constant-voltagecharging for 8 hours, in which the battery was charged up to 4.1 V by acurrent of 5 A and then charged by a constant voltage of 4.1 V. Then,the batteries were discharged up to 2.5 V by a constant current of 10 A.The discharge capacities of three batteries ranged between 23.1 and 23.3Ah but the capacities of two remaining batteries were 19.5 Ah and 14.3Ah and a slight short circuit was found. Because the comparative example6-1 did not use a second separator, the electrode packing rate wasimproved compared with the case of the embodiment 6-1 but a slight shortcircuit easily occurred through the initial capacity was high. TABLE 5Thick- Porosity ness Pressure at 2.5 Unit Sepa- A F kg/cm² weight ratorMaterial (mm) (kg/cm²) (%) (g/m²) Embodi- First Polyethyl- 0.087 0.50089.1 13.7 ment sepa- ene-poly- 6-1 rator propylene non- woven fabricSecond Polyethyl- 0.025 <0.025 41.0 15.5 sepa- ene micro- rator porousfilm Embodi- First Polypro- 0.072 0.050- 83.0 13.1 ment sepa- pylene0.075 6-2 rator non- woven fabric

[Positioning of Electrode Unit]

A preferred embodiment of the present invention for positioning anelectrode unit using a separator is described below. In the case of thisembodiment, a separator 104 is bonded to a positive electrode 101 aand/or negative electrodes 101 b and 101 c.

It has been very difficult so far to stack a positive electrode, anegative electrode, and a separator having a size of 272×182 mm largerthan the negative electrode while accurately positioning them which havedifferent size to each other. However, this embodiment makes it possibleto solve the above problem by bonding at least one of a plurality ofseparators to a positive or negative electrode or to both positive andnegative electrodes. In this case, it is more preferable to bond aplurality of separators to a positive or negative electrode or to bothpositive and negative electrodes or particularly preferable to bond allseparators to a positive or negative electrode or to both positive andnegative electrodes. This embodiment solves the above problem by bondingthe separator 104 of this embodiment to the positive electrode 101 aand/or negative electrodes 101 b and 101 c. When setting dimensions ofthe positive electrode 101 a to 268×178 mm, it is necessary to makedimensions of the negative electrodes 101 b and 101 c slightly largerthan those of the positive electrode 101 a in order to preventdeposition of lithium on a negative electrode. For example, it isnecessary to adjust dimensions of the negative electrodes 101 b and 101c to 270×180 mm.

Specifically, as shown in FIGS. 11A to 11C, a positive electrode unit111 a is formed by bonding a positive electrode 101 a with a separator104, a negative electrode unit 111 b is formed by bonding a negativeelectrode 101 b with the separator 104, and a single-sided negativeelectrode unit 111 c is formed by bonding a single-sided negativeelectrode 101 c with the separator 104. In this case, the size of theseparator 104 is equal to each other irrelevant to the sizes of thepositive electrode 101 a and negative electrodes 101 b and 101 c.Therefore, by aligning only the separator 104, it is possible to easilystack the positive electrode 101 a, negative electrodes 101 b and 101 chaving different sizes, and separator 104.

Because the separator 104 is not shifted when bonding it with thepositive electrode 101 a or negative electrodes 101 b and 101 c, it ispossible to make the size of the separator 104 equal to the size of thenegative electrodes 101 b and 101 c. By removing the portion of aseparator protruding beyond the electrodes, it is possible to improvethe electrode packing efficiency corresponding to the size of theremoved portion. A case is described above in which the separator 104 isbonded to the positive electrode 101 a or negative electrodes 101 b and101 c which are previously cut into predetermined dimensions. However,bonding of a separator is not limited to the above case. For example, itis possible to bond a separator to hoop electrodes and then cut theelectrodes. Thus, it is possible to use various methods.

A method for bonding the separator 104 with the positive electrode 101 aand/or negative electrodes 101 b and 101 c is not limited. However, itis important that all or most of pores of the separator 104 are notblocked (the separator does not have electron conductivity as rawmaterial, and thus it must hold an electrolyte and have pores throughwhich ions held in the electrolyte move between positive and negativeelectrodes). Namely, it is important that electrolyte passages aresecurely maintained to hold the penetration through the separator 104from the front surface to the rear surface.

Specifically, methods for bonding the separator 104 with the positiveelectrode 101 a and/or negative electrodes 101 b and 101 c includemechanical bonding by pressing, bonding due to fusion of a part of aseparator, bonding by chemicals, and bonding by adhesive and so on.Particularly, it is preferable to fuse a separator by heat and bond itwith an electrode because impurities are not contained, the separator isnot easily creased, and moreover warpage or burr of the electrodeproduced due to a slit or the like can be corrected at the same time. Inthis case, it is possible to easily bond a separator made ofpolyethylene having a low fusing point. In the case of non-woven fabric,when using a composite separator made of materials having differentfusing points, for example, when using polypropylene as the corematerial of fiber and polyethylene as an external layer or mixingpolyethylene powder in polypropylene non-woven fabric, it is possible tomore easily bond the separator without closing pores of the separator. Amethod of mixing polyethylene into an electrode and bonding apolypropylene separator is a simple method.

When bonding a separator with an electrode by fusing the separator, itis preferable to heat the electrode so that the very surface of theseparator is fused when the separator contacts the electrode. In thiscase, it is possible to bond the separator with the electrode by heatingthe electrode up to a temperature equal to the fusing point of theseparator or higher and pressing them in a short time without closingpores of the separator. In this case, it is not necessary that theentire surface of the electrode is bonded with the entire surface of theseparator. It is allowed that a part of the electrode is bonded with apart of the separator so that their position is not shifted when thebattery is formed.

The bonding structure of the positive electrode 101 a, negativeelectrodes 101 b and 101 c, and separator 104 is effective when stackingpluralities of electrodes and separators whose positioning isparticularly difficult, particularly when stacking five electrodes ormore and five separators or more, however it is possible to use thisstructure for other cases.

Embodiments for positioning an electrode unit using a spacer are morespecifically described below.

Embodiment 7- 1

(1) A positive-electrode mixture slurry was obtained by mixing 100 partsby weight of LiCO₂O₄, 8 parts by weight of acetylene black, and 3 partsby weight of polyvinylidene fluoride (PVdF) with 100 parts by weight ofN-methylpyrrolidone (NMP). A positive electrode was obtained by applyingthe slurry to both sides of aluminum foil having a thickness of 20 μmserving as a current collector, and drying and pressing the foil. FIG. 6is an illustration of an electrode. In the case of this embodiment, thecoating area (W1×W2) of the electrode 101 was 268×178 mm² and slurry wasapplied to both sides of the current collector 102 of 20 μm thickness ata thickness of 95 μm. As a result, the electrode thickness t was 210 μm.One of the edge portions of the shorter side of the current collector102 was not coated in 1 cm width and a tab 103 (aluminum with athickness of 0.1 mm and a width of 6 mm) was welded.

(2) A negative-electrode mixture slurry was obtained by mixing 100 partsby weight of graphitized mesocarbon microbeads (MCMB, made by OSAKA GASCHEMICAL Co., Ltd., product No. 6-28) and 10 parts by weight of PVdFwith 90 parts by weight of NMP. A negative electrode was obtained byapplying the slurry to both sides of copper foil having a thickness of14 μm serving as a current collector, drying the foil and then pressingthe foil. Because the shape of the electrode is the same as that of theabove-described positive electrode, the negative electrode is describedbelow by referring to FIG. 6. In the case of this embodiment, thecoating area (W1×W2) of the electrode 101 is 270×180 mm² and the slurrywas applied to both sides of the current collector 102 of 14 μmthickness at a thickness of 105 μm. As a result, the electrode thicknesst was 224 μm. One of the edge portions of the shorter side of thecurrent collector 102 was not coated in 1 cm width and a tab 103(aluminum with a thickness of 0.1 mm and a width of 6 mm) was welded.

Slurry was applied to only one side in accordance with the same methodand a single-sided electrode having a thickness of 119 μm was formed inaccordance with the same method except for the single-sided applicationof the slurry. The single-sided electrode was set to the outermost ofthe electrode-stacked body in Item (3) (101 c in FIG. 2).

(3) A positive electrode unit 111 a, negative electrode unit 111 b, andsingle-sided negative electrode unit 111 c were formed by bonding aseparator 104 obtained by laminating polyethylene-polypropylenenon-woven fabric of 272×180 mm² (thickness of 87 μm) and a polypropylenemicro-porous film (thickness of 25 μm) to a positive electrode 101 a andnegative electrodes 101 b and 101 c at the positional relation shown inFIGS. 12A to 12C. Each electrode was bonded with thepolyethylene-polypropylene non-woven fabric side of the separator 104.Specifically, the separator 104 and electrodes (positive electrode 101 aand negative electrodes 101 b and 101 c) were stacked in the order at apredetermined position and heated from the electrode side by an iron atapproximately 140 degree Celsius to bond them. After bonding them, theseparator 104 was observed by removing it from some of the electrodeunits 111 a, 111 b, and 111 c. As a result, the state of surface poresof the separator 104 was hardly changed from the state before theseparator 104 was bonded. An electrode-stacked body was formed byalternately stacking eight positive-electrode units 111 a, sevennegative-electrode units 111 b, one single-sided negative-electrode unit111 c, one single-sided negative electrode 101 c not bonded with theseparator 104, and the separator 104 as shown in FIG. 10.

(4) The bottom case 2 of the battery (refer to FIG. 1) was formed bydeep drawing of a 0.5 mm thin plate made of SUS304 into a depth of 5 mm.The upper case 1 of the battery was also formed of a 0.5 mm thin platemade of SUS304. The positive and negative electrodes made of SUS304 3and 4 (diameter of 6 mm) were set to the upper case and a safety-venthole (diameter of 8 mm) was formed on the upper case but the positiveand negative electrodes 3 and 4 were insulated from the upper case 1 bya polypropylene packing.

(5) Each positive-electrode tab 103 a of the electrode-stacked bodyformed in the above Item (3) was welded to the positive-electrode tab 3and each negative-electrode tab 103 b of it was welded to thenegative-electrode tab 4 through a connection line and theelectrode-stacked body was set to the bottom case 2 and fixed by aninsulating tape to laser-weld the entire circumference of the corner Ain FIG. 1. Thereafter, a solution was made by dissolving LiPF₆ at aconcentration of 1 mol/l in a solvent obtained by mixing ethylenecarbonate and diethyl carbonate at a weight ratio of 1:1. The solutionwas poured through a safety-vent hole as an electrolyte and the uppercase was closed by aluminum foil having a thickness of 0.1 mm. The totalof five batteries were formed.

(6) The obtained battery was respectively charged by aconstant-current/constant-voltage charging for 8 hours, in which thebattery was charged up to 4.1 V by a current of 5 A and then charged bya constant voltage of 4.1 V. Then the batteries were discharged up to2.5 V by a constant current of 10 A. Discharge capacities ranged between21.3 and 21.5 Ah. The temperature rise of the batteries while dischargedwas small compared with the case of a prismatic battery (battery havinga thickness of 12 mm or more) having the same capacity.

COMPARATIVE EXAMPLE 7-1

Five batteries were formed similarly to the case of the embodiment 7-1except that a separator was not bonded. The obtained battery was chargedby a constant-current/constant-voltage charging for 8 hours, in whichthe battery was charged up to 4.1 V by a current of 5 A and then chargedby a constant voltage of 4.1 V. Then, the batteries were discharged upto 2.5 V by a constant current of 10 A. Discharge capacities of threebatteries ranged between 20.9 and 21.3 Ah but those of two remainingbatteries were 18.5 and 14.3 Ah and a slight short circuit occurred.

Now, description of positioning of A- and B-type separators and anelectrode unit using a separator is completed.

A preferable control method of the above secondary batteries of thepresent invention is described below by referring to the accompanyingdrawings. FIG. 13 shows a secondary battery 111 embodying the presentinvention. The battery 111 is provided with a positive terminal 112 pand a negative terminal 112 n. These positive and negative terminals aregenerally attached to a battery. Charge and discharge of a battery havebeen controlled so far by measuring the voltage, internal resistance,current between these two terminals, etc. A battery of the presentinvention is further provided with operation-characteristic measuringterminals 113 p, 113 n, 114 p, and 114 n for measuring internalinformation of the battery. For example, fluctuation of temperatures ina battery can be measured by connecting the end of a thermocouplereaching the central portion of the battery to the positive and negativeterminals 113 p and 113 n and thereby measuring the temperature of theinner portion of the battery, moreover connecting the end of athermocouple located nearby the surface of the battery to the positiveand negative terminals 114 p and 114 n and thereby measuring thefluctuation of temperatures in the battery, and comparing these measuredvalues. Voltages in the battery can be measured by connectingvoltage-measuring lines extending from different portions of the batteryto the terminals 113 p, 113 n, 114 p, and 114 n and measuring thepotential difference from the positive terminal 112 p. Furthermore, itis possible to measure the voltage fluctuation in the battery bymeasuring voltages between the terminals 113 p to 113 n and between theterminals 114 p to 114 n. Data signals thus measured are sent to acontrol unit through connection lines AA1 to AAn in the block diagram(FIG. 14) to determine the fluctuation degree by the control unit,output a command for changing charge and discharge conditions orstopping charge and discharge to a charge-and-discharge control unit, oroutput a cooling-fan operating command and other operation controlcommands in accordance with the fluctuation degree. As a result, even iffluctuation of operation characteristics occurs in the battery, it ispossible to eliminate or moderate the fluctuation or prevent thedeterioration of the safety or reliability due to the fluctuation, byconducting a control in accordance with the fluctuation.

A control method of the present invention is used for a household energystorage system (for nighttime power storage, cogeneration, photovoltaicpower generation, or the like) or a energy storage system of an electricvehicle and a secondary battery used for the system has a large capacityand a high energy density. It is preferable for the secondary battery tohave an energy capacity of 30 Wh or more or it is more preferable forthe secondary battery to have an energy capacity of 50 Wh or more. It ispreferable for the secondary battery to have a volume energy density of180 Wh/l or more or it is more preferable for the secondary battery tohave a volume energy density of 200 Wh/l. When the energy capacity isless than 30 Wh or the volume energy density is lower than 180 Wh/l,this method is not preferable because the capacity is too small to beused for a energy storage system it is necessary to increase the numbersof batteries connected in series and in parallel in order to obtain asufficient system capacity, or a compact design becomes difficult.

From the above viewpoints, a nickel-hydrogen battery or a lithiumsecondary battery provided with a rion-aqueous electrolyte containinglithium salt is preferable as a secondary battery of the presentinvention and particularly, a lithium secondary battery is optimum.

It is preferable to use materials, dimensions, and shapes ofsecondary-battery components such as a positive electrode, negativeelectrode, separator, and the plate thickness of a battery case havingthe characteristics already described.

A secondary battery of the present invention is characterized bymeasuring the fluctuation of operation characteristics produced in abattery and controlling the battery in accordance with the measurementresult. Operation characteristics to be measured include not onlycharacteristics directly related to charge and discharge operations suchas voltage, current, temperature, and internal resistance but alsocharacteristics indirectly related to charge and discharge operationssuch as dimension and pressure to be changed due to gas generationcaused under severe operations. It is possible to use various measuringmeans normally used for these characteristics for measurement. Thoughthe number of measuring points in a battery (in a single cell) isdetermined in accordance with the shape of a battery, requested controlaccuracy, or measuring means, it is preferable to measure at least oneoperation characteristic at at least 2 points and compare measurementresults.

For example, when selecting a voltage as an operation characteristic tobe measured, it is possible to know the fluctuation of voltages in abattery by measuring voltages at a plurality of points of the battery ormeasuring an electrode terminal voltage and a voltage at one point orvoltages at a plurality of points of the battery and comparing them.When measuring temperature as an operation characteristic, it ispossible to know the fluctuation of temperatures in a battery bycomparing the temperatures at a plurality of points such as the innerportion and the vicinity of the surface of a battery, a terminal and thesurface of a battery case, an upper portion a and lower portion of abattery case, and so on. When measuring a dimensional change of abattery case, it is possible to easily know the state of a battery bymeasuring the thickness of the battery. In this case, it is possible toknow the fluctuation of dimensions of a battery, particularly thefluctuation of dimensional changes by measuring a plurality of batterythicknesses from the outside of the battery and comparing the measuredthicknesses.

It is possible to combine measurements of a plurality of operationcharacteristics. From the viewpoint of measurement efficiency, however,it is preferable to minimize the number of measuring points by selectingmeasuring points representing fluctuations of operation characteristicsof a battery.

In the case of a control method of the present invention, fluctuation ofoperation characteristics of a secondary battery is controlled so as toeliminate or moderate the fluctuation or prevent the deterioration ofthe safety and reliability. Control can be performed by various methodsin accordance with the sort of operation characteristics. For example,when the fluctuation of differences between surface temperature andinternal temperature is measured and it is determined that thefluctuation must be moderated, controls are performed to lower thecurrent of charge and discharge, to operate a cooling of a fan, or tostop charge or discharge according to the circumstances. Whenfluctuation of internal resistances between electrodes in a batteryoccurs, there are some cases in which current is concentrated on aportion having a small internal resistance and local overcharge occurs.In this case, by performing controls of pressing from the outside of abattery case and reduction of charge rate, it is possible to preventlocal overcharge and secure the safety depending on the fluctuation ininternal resistance.

The method of the present invention for controlling a secondary batteryfor a energy storage system can be applied to each cell or the cellsselected according to a necessity in a module formed by combining aplurality of single cells or in a battery system formed by combining themodules. In this case, as a control mode, it is possible to useconventionally proposed cell basis control or module basis controltogether with cell by cell control of the present invention. Further, itis possible to control a module or battery system by utilizing thefluctuation information regarding each of different cells. For example,when each of the cells shows similar operation-characteristic,simultaneous control can be performed for each of the modules or wholeof the battery system.

It is possible to perform the control according to a safety requirementrelated to the amount of charged or discharged energy, in such a mannerthat in a usual state charge or discharge is controlled based on anoperation characteristic, e.g. the measurement of the voltage of aposition of a battery, and a control based on a temperature measurementis added when the amount of charged or discharged energy has increased,and a control base on a dimension measurement is added when the amounthas further increased.

In the case of a secondary-battery control method of the presentinvention, a battery is charged by charging equipment such as aphotovoltaic cells, a commercial power system, or an electric generator,etc., and is discharged for loads such as a motor, an electric lamp, ahousehold unit, etc. Therefore, it is possible to perform a control byutilizing the operational information of the unit or equipment, or tooperate the unit or equipment in accordance with the state of thebattery.

In the case of the above-described secondary-battery control method ofthe present invention, it is possible to improve the reliability andsafety by performing control corresponding to the fluctuation ofoperation characteristics in a battery. However, it is preferable todesign a battery so as to reduce the fluctuation of operationcharacteristics in the battery. Therefore, in the case of the presentinvention, a battery is formed into a flat shape and the thickness ofthe battery is preferably less than 12 mm, more preferably less than 10mm, and still more preferably less than 8 mm. When the thickness of abattery is 12 mm or more, it is difficult to radiate the heat in thebattery to the outside or the temperature difference between the innerportion and the surface of the battery increases, the fluctuation in thebattery increases, and control becomes complicated.

A control method of the present invention is more specifically describedbelow based on an embodiment of the control method.

Embodiment 8-1

(1) Positive-electrode mixture slurry was obtained by mixing 100 partsby weight of spinel-type LiMn₂O₄ (made by SEIMI CHEMICAL; product No.M063), 10 parts by weight of acetylene black, and 5 parts by weight ofpolyvinylidene fluoride (PVdF) with 100 parts by weight ofN-methylpyrrolidone (NMP). A positive electrode was obtained by applyingthe slurry to both sides of aluminum foil having a thickness of 20 μmand drying and pressing the foil. FIG. 15 is an illustration of anelectrode. In the case of this embodiment, the coating area (W1×W2) ofan electrode 1101 was 133×198 mm² and slurry was applied to both sidesof 20-μm aluminum foil 1102 at a thickness of 120 μm. As a result, theelectrode thickness was 260 μm. One of the edge portions of the currentcollector extending along the arrow W2 and having a width of 1 cm wasnot coated with the electrode, and a tab 1103 (aluminum having athickness of 0.1 mm and a width of 6 mm) was welded thereto.

(2) Negative-electrode mixture slurry was obtained by mixing 100 partsby weight of graphitized mesocarbon microbeads (MCMB: made by OSAKA GASCHEMICAL Co., Ltd.; product No. 628) and 10 parts by weight of PVdF with90 parts by weight of NMP. A negative electrode was obtained by applyingthe slurry to both sides of copper foil having a thickness of 14 μm anddrying and pressing the foil. Because the shape of the negativeelectrode is the same as the above positive electrode, the negativeelectrode is described by referring to FIG. 15. In the case of thisembodiment, the coating area (W1×W2) of the electrode 1101 was 135×200mm² and the slurry was applied to both sides of the copper foil 1102 ata thickness of 80 μm. As a result, the electrode thickness t is 174 μm.One of the edge portions of the current collector extending along thearrow W2 and having a width of 1 cm is not coated with the electrode,and a tab 1103 (nickel having a thickness of 0.1 ×mm and a width of 6mm) is welded thereto.

Slurry was applied to only one side by the same method and asingle-sided electrode having a thickness of 94 μm was formed by thesame method other than the side. The single-sided electrode is set tothe outermost of the electrode-stacked body in the following Item (3)(1101 n in FIG. 17).

(3) Two electrode-stacked bodies were formed by alternately stackingnine positive electrodes 1101p and ten negative electrodes (eightboth-sided electrodes 1101 n and two single-sided electrodes 1101 n′)obtained in the above Item (1) with a separator 1104 (made by TONENTAPIRUSU Co., Ltd.; made of porous polyethylene) held between theelectrode as shown in FIG. 17.

(4) The battery bottom case (122 in FIG. 16) was formed by deep-drawinga thin plate made of SUS304 having a thickness of 0.5 mm. A battery caseupper case (121 in FIG. 16) was also formed of a thin plate made ofSUS304 having a thickness of 0.5 mm.

Terminals 113 and 114 made of SUS304 (diameter of 6 mm) and asafety-vent hole 117 (diameter of 8 mm) were formed on the battery caseupper case, and the terminals 113 and 114 were insulated from thebattery case upper case 111 by a polypropylene packing.

(5) Each of the positive terminals 1103 p of two electrode-stackedbodies formed in the above Item (3) was welded to the terminal 113 andeach of the negative electrodes 1103 n of the bodies was welded to theterminal 114 and then, the electrode-stacked bodies were stacked on thebattery bottom case 122 and fixed by an insulating tape. To measuretemperatures of portions X and Y in FIG. 17, a film thermocouple made byPhillips Corp. was attached to the negative-electrode current collectorof each portion and the lead wire of each thermocouple was connected tothe positive electrodes 115 p and 116 p and negative electrodes 115 nand 116 n. A spacer 1105 was present between two stacked bodies in orderto form a space for accommodating the Y-portion thermocouple. Under theabove state, the entire circumference of the portion A in FIG. 16 waslaser-welded. Thereafter, a solution made by dissolving LiPF₆ at aconcentration of 1 mol/l in a solvent obtained by mixing ethylenecarbonate and diethyl carbonate at a weight ratio of 1:1 was pouredthrough a safety-vent hole as an electrolyte and hole was closed byusing aluminum foil having a thickness of 0.1 mm. It is possible tomeasure the temperature nearby the surface in the battery in accordancewith the potential difference between the positive and negativeterminals 115 p and 115 n and the temperature of the inner portion inthe battery in accordance with the potential difference between 116 pand 116 n and to measure the temperature fluctuation in the battery bycomparing the above potential differences.

(6) The formed battery has dimensions of 165×230 mm² and a thickness of10 mm. The obtained battery was charged by aconstant-current/constant-voltage charging for 8 hours, in which thebattery was charged up to 4.3 V by a current of 10 A and then charged bya constant voltage of 4.3 V. Then, the battery was discharged up to 2.0V by a current of 30 A. The discharge capacity was 22 Ah, energycapacity was 78 Wh, and energy density was 205 Wh/l.

(7) The battery was charged and discharged under the conditions in theabove Item (6) while measuring temperatures of the X and Y portions.However, when a difference occurred between internal temperature andexternal temperature, charge or discharge was stopped and charge anddischarge were repeated so that the fluctuation of internal and externaltemperatures did not occur. As a result, charge and discharge could beperformed up to 10 cycles.

COMPARATIVE EXAMPLE 8-1 For Comparison With Embodiment 8-1

Charge and discharge were repeated 10 times by using a battery andcharge and discharge conditions same as the case of the embodiment undera constant condition without control according to measurement of theinternal temperature of the battery. As a result, the thickness of thebattery was increased and the internal resistance was raised.

Embodiment 8-2

(1) Positive-electrode mixture slurry was obtained by mixing 100 partsby weight of spinel-type LiMn₂O₄ (made by SEIMI CHEMICAL; product No.M063), 10 parts by weight of acetylene black, and 5 parts by weight ofPVdF with 100 parts by weight of NMP. A positive electrode was obtainedby applying the slurry to both sides of aluminum foil having a thicknessof 20 μm and drying and pressing the foil. FIG. 18 is an illustration ofan electrode. In the case of this embodiment, the coating area (W1×W2)of an electrode 1201 was 258×168 mm² and slurry was applied to bothsides of 20-μm aluminum foil 1202 at a thickness of 120 μm. As a result,the electrode thickness t was 260 μm. Both of the edge portions and thecentral portion of the current collector in the view of the longitudinaldirection of the collector was not coated with the electrode in thewidth of 1 cm, and a tabs 1203 a, 1203 b, and 1203 c (aluminum having athickness of 0.1 mm and a width of 4 mm) was welded thereto.

A measuring electrode having measuring electrodes 1204 a, 1204 b, and1204 c was formed in order to measure the fluctuation of internalvoltages. The electrode was formed by welding a 3 mm-square expand metal(aluminum) having a thickness of 50 μm to one end of a slender piece ofstainless-steel foil having a width of 3 mm and a thickness of 10 μm,attaching the expand metal to the surface of a positive electrode in abattery, bonding the stainless-steel foil to the positive electrodewhile insulating it from the positive electrode, and positioning theother end of the piece of the foil to protrude beyond an edge of thepositive electrode to form a terminal.

(2) Negative-electrode mixture slurry was obtained by mixing 100 partsby weight of graphitized mesocarbon microbeads (MCMB) and 10 parts byweight of PVdF with 90 parts by weight of NMP. A negative electrode wasobtained by applying the slurry to both sides of a copper foil having athickness of 14 μm and drying and pressing the foil. Because the shapeof the negative electrode is the same as the above positive electrode,the negative electrode is described by referring to FIG. 18. In the caseof this embodiment, the coating area (W1×W2) of the electrode 1201 is260×170 mm² and the slurry was applied to both sides of the copper foil1202 of 14 μm at a thickness of 80 μm. As a result, the electrodethickness t was 174 μm. Both of the edge portions and the centralportion of the current collector in the view of the longitudinaldirection of the collector was not coated with the electrode in thewidth of 1 cm, and a tabs 1203 a′, 1203 b′, and 1203 c′ (copper having athickness of 0.1 mm and a width of 4 mm) was welded thereto.

To measure the fluctuation of internal voltages, measuring electrodeshaving protruded ends as measuring electrodes 1204 a′, 1204 b′, and 1204c′ were formed, in the same manner as in the positive electrode, bywelding a 3 mm-square expand metal (copper) having a thickness of 50 μmto an end of a slender piece of stainless-steel foil having a width of 3mm and a thickness of 10 μm.

Furthermore, slurry was applied to only one side by the same method anda single-sided electrode having a thickness of 94 μm was formed by thesame method other than the single-sided application of the slurry. Thesingle-sided electrode was set to the outermost of the electrode-stackedbody stated in the following Item (3) (1201 n′ in FIG. 19).

(3) An electrode-stacked body was formed by alternately stacking tenpositive electrodes 1201 p and eleven negative electrodes (nineboth-sided electrodes 1201 n and two single-sided electrodes 1201 n′)obtained in the above Item (1) with a separator 1205 (made by TONENTAPIRUSU Co., Ltd.; made of porous polyethylene) held between each ofthe electrode as shown in FIG. 19. A separator made of polypropylenenon-woven fabric having a thickness of 100 μm was set between electrodesprovided with internal-potential measuring terminals. The positiveelectrodes and negative electrodes were stacked so that their terminalsprotrude in mutually opposite direction.

(4) A battery bottom case (same as symbol 122 in FIG. 16) was formed bydeep-drawing a thin plate made of SUS304 having a thickness of 0.5 mm.The battery upper case (symbol 1211 in FIG. 20) was also formed of athin plate made of SUS304 having a thickness of 0.5 mm. The followingwere formed on the battery upper case as shown in FIG. 20:charge-discharge terminals 1213 a, 1213 b and 1213 c, 1214 a, 1214 b and1214 c (diameter of 6 mm) which were made of SUS304, voltage-measuringterminals 1215 a, 1215 b and 1215 c, and 1216 a, 1216 b and 1216 c(diameter of 3 mm), and a safety-vent hole 117 (diameter of 8 mm). Theterminals 1213 a, 1213 b and 1213 c, and 1214 a, 1214 b and 1214 c, 1215a, 1215 b and 1215 c, and 1216 a, 1216 b and 1216 c were insulated fromthe battery upper case 1211 by a polypropylene packing.

(5) A series of charge-discharge positive and negative electrodes andtheir positive-electrode- and negative-electrode-voltage measuringterminals on two electrode stacked bodies formed in the above Item (3)were welded to connection terminals on the battery case throughconnection lines as shown below. Connection terminal on Terminal ofelectrode-layered body battery case Charge-discharge positive-electrodetab 1203a Terminal 1213a Charge-discharge positive-electrode tab 1203bTerminal 1213b Charge-discharge positive-electrode tab 1203c Terminal1213c Charge-discharge negative-electrode tab 1203a Terminal 1214aCharge-discharge negative-electrode tab 1203b′ Terminal 1214bCharge-discharge negative-electrode tab 1203c′ Terminal 1214cPositive-electrode measuring electrode 1204a Terminal 1215aPositive-electrode measuring electrode 1204b Terminal 1215bPositive-electrode measuring electrode 1204c Terminal 1215cNegative-electrode measuring electrode 1204a′ Terminal 1216aNegative-electrode measuring electrode 1204b′ Terminal 1216bNegative-electrode measuring electrode 1204c′ Terminal 1216c

Thereafter, the electrode-stacked bodies were stacked on the bottom ofthe battery bottom case 122 and fixed by an insulating tape, and theentire circumference of a portion corresponding to the edgy portion A inFIG. 16 was laser-welded. Thereafter, a solution was made by dissolvingLiPF₆ at a concentration of 1 mol/l in a solvent obtained by mixingethylene carbonate and diethyl carbonate at a weight ratio of 1:1. Thesolution was poured through a safety-vent hole 117 as an electrolyte andthe hole was closed by using aluminum foil having a thickness of 0.1 mm.

(6) The formed battery has dimensions of 300×210 mm² and a thickness of6 mm. The battery was charged and discharged so that a potentialdifference did not occur between the positive-electrode-voltagemeasuring terminals 1215 a, 1215 b, and 1215 c or between thenegative-electrode-voltage measuring terminals 1216 a, 1216 b, and 1216c by measuring the potential difference between thepositive-electrode-voltage measuring terminals 1215 a, 1215 b, and 1215c and the potential difference between the negative-electrode-voltagemeasuring terminals 1216 a, 1216 b, and 1216 c and controlling thecurrent to be supplied to the charge-discharge terminals (positiveterminals 1213 a, 1213 b, and 1213 c and the negative terminals 1214 a,1214 b, and 1214 c). That is, charge and discharge were controlled so asto eliminate the fluctuation of potentials for charge and discharge incells. The battery was charged by a constant-current/constant-voltagecharging for 8 hours, in which the battery was charged up to 4.3 V(potential between terminals 1213 b and 1214 b) by a current of 10 A andthen charged by a constant voltage of 4.3 V.

Then, the battery was discharged up to 2.0 V by a constant current of 5A. The discharge capacity was 23 Ah, energy capacity was 81 Wh, andvolume energy density was 210 Wh/l.

(7) Charge and discharge were repeated 10 times while performing theabove control. For comparison, the same level of charge and dischargewere repeated 10 times only by the connection to the terminal andelectrode 1213 a and 1214 a. As a result, the battery controlled inaccordance with the method of the embodiment was less deteriorated incapacity. Now, description of methods of the present invention iscompleted.

As described above, according to the present invention, it is possibleto provide a non-aqueous secondary battery applicable to energy storagewhich has a large capacity of 30 Wh or more and a volume energy densityof 180 Wh/l or more and is superior in heat radiation characteristic andsafely used. By a specific negative electrode provided, it is possibleto provide a non-aqueous secondary battery applicable to energy storagesystem and having features of large capacity and high safety.

Furthermore, according to the present invention, it is possible toprovide a flat non-aqueous secondary battery, particularly a flatbattery having a large capacity and a high volume energy density, whichis further superior in cycle characteristic by comprising one type ofseparator or two types or more of separators having a specificresiliency.

Furthermore, according to the present invention, it is possible toprovide a flat non-aqueous secondary battery, particularly a flatbattery having a large capacity and a high volume energy density, whichis superior in heat radiation characteristic, and has a low probabilityof making short circuit during assembling of a battery based on thebonding of a separator with an electrode.

Furthermore, according to a control method of the present invention,reliabilities such as safety and cycle characteristic of a battery arefurther improved because of measuring the fluctuation of operationcharacteristics in the battery and controlling charge and discharge inaccordance with the measurement results.

Furthermore, according to a secondary battery of the present inventionprovided with positive and negative terminals for charge and dischargeand terminals for measuring internal operation characteristics, it ispossible to easily and securely perform the above control.

1. A non-aqueous secondary battery comprising positive and negativeelectrodes and a lithium salt-containing electrolyte, the battery beingat least 30 Wh in energy capacity and at least 180 Wh/l in volume energydensity and having a flat shape with a thickness of less than 12 mm. 2.The non-aqueous secondary battery according to claim 1, wherein thepositive electrode contains manganese oxide.
 3. The non-aqueoussecondary battery according to claim 1, wherein the negative electrodeis formed by using graphite having an average particle diameter of 1 to50 μm as active material, a resin as binder, and a metal as currentcollector, the negative electrode having a porosity of 20 to 35%, anelectrode density of 1.40 to 1.70 g/cm³, and an capacity of electrode of400 Ah/cm³ or higher.
 4. The non-aqueous secondary battery according toclaim 3, wherein the negative electrode contains a graphite materialobtained by graphitizing mesocarbon microbeads.
 5. The non-aqueoussecondary battery according to claim 1, wherein the negative electrodecomprises as active material double-structure graphite particles formedwith graphite-based particles and amorphous carbon layers covering thesurface of the. graphite-based particles, the graphite-based particleshaving (d002) spacing of (002) planes of not more than 0.34 nm asmeasured by X-ray wide-angle diffraction method, the amorphous carbonlayers having (d002) spacing of (002) planes of 0.34 nm or higher. 6.The non-aqueous secondary battery according to claim 5, wherein thenegative electrode is formed by using double-structure graphiteparticles having an average particle diameter of 1 to 50 μm as activematerial, a resin as binder, and a metal as current collector, thenegative electrode having a porosity of 20 to 35%, an electrode densityof 1.20 to 1.60 g/cm³, and an capacity of electrode of 400 mAh/cm³ orhigher.
 7. The non-aqueous secondary battery according to claim 1,wherein the negative electrode comprises as active material a carbonmaterial manufactured by mixing at least one of artificial graphite andnatural graphite with a carbon material having volatile components onthe surface and/or in the inside and baking the mixture.
 8. Thenon-aqueous secondary battery according to claim 7, wherein the negativeelectrode is formed by using a resin as binder and a metal as currentcollector, the negative electrode having a porosity of 20 to 35%, anelectrode density of 1.20 to 1.60 g/cm³, and an capacity of electrode of400 mAh/cm³ or higher.
 9. The non-aqueous secondary battery according toclaim 1, wherein the front and rear sides of the flat shape arerectangular.
 10. The non-aqueous secondary battery according to claim 1,wherein the wall thickness of a battery case of the non-aqueoussecondary battery is not less than 0.2 mm and not more than 1 mm.
 11. Asecondary battery comprising a positive electrode, a negative electrode,a separator, and a non-aqueous electrolyte containing lithium salt andhaving a flat shape.
 12. The non-aqueous secondary battery according toclaim 11, wherein when a pressure of 2.5 kg/cm² is applied to thedirection of thickness of the separator, the thickness A of theseparator is not less than 0.02 mm and not more than 0.15 mm and theporosity of the separator is 40% or higher, and when the absolute valueof a change rate of the thickness (mm) of the separator relative to thepressure (kg/cm²) applied to the direction of thickness of the separatoris defined as B (mm/(kg/cm²)), the pressure F which renders B/A=1 is notless than 0.05 kg/cm² and not more than 1 kg/cm².
 13. The non-aqueoussecondary battery according to claim 11, wherein the separator has afirst separator and a second separator different from the firstseparator, when a pressure of 2.5 kg/cm² is applied to the direction ofthickness of the separator, the thickness A of the first separator isnot less than 0.02 mm and not more than 0.15 mm and the porosity of thefirst separator is 40% or higher, and when the absolute value of achange rate of the thickness (mm) or the first separator relative to thepressure (kg/cm²) applied to the direction of thickness of the firstseparator is defined as B (mm/(kg/cm²)), the pressure F which rendersB/A=1 is not less than 0.05 kg/cm² and not more than 1 kg/cm², and thesecond separator is micro-porous film having a thickness of 0.05 mm orless, a pore diameter of 5 mm or less, and a porosity of 25% or more.14. The non-aqueous secondary battery according to claim 11, wherein theseparator is bonded with the positive electrode and/or the negativeelectrode.
 15. The non-aqueous secondary battery according to claim 14,wherein the separator is bonded with the positive electrode and thenegative electrode by fusing part of the separator and, passages for thenon-aqueous electrolyte are formed to penetrate the separator from thefront side surface to the rear side surface thereof.
 16. The non-aqueoussecondary battery according to claim 12, wherein the non-aqueoussecondary battery has a flat shape with a thickness of less than 12 mmand is at least 30 Wh in energy capacity and at least 180 Wh/l in volumeenergy density.
 17. The non-aqueous secondary battery according to claim12, wherein the front side and the rear side of the flat shape arerectangular.
 18. The non-aqueous secondary battery according to claim12, wherein the wall thickness of a battery case of the non-aqueoussecondary battery is not less than 0.2 and not more than 1 mm.
 19. Thenon-aqueous secondary battery according to claim 12, wherein theseparator is made of a material comprising at least one of polyethyleneor polypropylene as a main component. 20-29. (canceled)
 30. A secondarybattery for a energy storage system, comprising positive and negativeterminals for charge and discharge provided on the battery case andoperation-parameter measuring electrodes extending from differentportions of the battery to the outside of the battery case formeasurement of the operation parameters in the battery.